Skype
From Wikipedia, the free encyclopedia
Skype (IPA pronunciation: /skʌɪp/, rhymes with type) is a proprietary peer-to-peer Voice over IP (VoIP) network founded by the entrepreneurs Niklas Zennström and Janus Friis, also founders of the file sharing application Kazaa. It competes against existing open VoIP protocols such as SIP, IAX, and H.323. The Skype Group, acquired by eBay in October 2005, is headquartered in Luxembourg, with offices in London, Tallinn and Prague[1].
Skype has experienced rapid growth in both popular usage and software development since launch, both of its free and its paid services. The Skype communications system is notable for its broad range of features, including free voice and video conferencing, and its ability to use peer to peer (decentralized) technology to overcome common firewall and NAT (Network address translation) problems.
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[edit] System and software
[edit] Technology
Skype users essentially make telephone calls and video calls through their computer using Skype software and the internet. The basis of the system is free communication between users of Skype software; however the product also allows Skype users to communicate with users of regular landline and mobile telephones. This software is currently available free of charge and can be downloaded from the company website, but the software is proprietary and the Skype protocol is unpublished.
The main difference between Skype and other VoIP clients is that Skype operates on a peer-to-peer model, rather than the more traditional server-client model. The Skype user directory is entirely decentralised and distributed among the nodes in the network, which means the network can scale very easily to large sizes (currently just over 100 million users) without a complex and costly centralised infrastructure.
Skype also routes calls through other Skype peers on the network to ease the traversal of Symmetric NATs and firewalls. This, however, puts an extra burden on those who connect to the Internet without NAT, as their computers and network bandwidth may be used to route the calls of other users.
The selection of intermediary computers is fully automatic, with individual users having no option to disable such use of their resources.
This fact is not clearly communicated however and seems to contradict the license agreement, which limits Skype's usage of the user's "processor and bandwidth [to the] purpose of facilitating the communication between [the user] and other Skype Software users" (section 4.1).
The Skype code is closed source, and the protocol is not standardized but proprietary; this has raised suspicion and drawn some criticism from software developers and users.[citation needed]
The Skype client's application programming interface (API) opens the network to software developers. The Skype API allows other programs to use the Skype network to get "white pages" information and manage calls.
The Windows user interface was developed in Pascal using Delphi, the Linux version is written in C++ with Qt, and the Mac OS X version is written in Objective-C with Cocoa.[2] Parts of the client use Internet Direct (Indy), an open source socket communication library.
[edit] Security
Skype generates a significant amount of discussion on how secure its traffic really is. It has had an impact upon the security and culture of VoIP telephony because of this discussion and several design principles:
- All Skype traffic is encrypted by default and the user cannot turn it off.[citation needed]
- Skype reportedly uses openly available, strong encryption algorithms.[3]
- The user is not involved in the encryption process and therefore does not have to deal with the issues of Public key infrastructure.
This has had an effect upon the rest of the market as they seek to offer competitive products. The security of internet communication has become an issue of which people are more aware and secure communication a feature they want to see in the products they use.
[edit] General
Since the Skype code is proprietary and closed source, the security of the software cannot be firmly established by independent experts; thus, its users—experts and non-experts alike—may base their usage of the product on merely trusting the manufacturer and behavior of the software downloaded from sources authorized by the manufacturer. In 2004, Niklas Zennstrom, co-founder of Skype, appeared to admit in an article on The Register that the current security model used a relatively short key size, relied upon security through obscurity, and would not withstand open-source scrutiny:
Would he make Skype open-source?
No, that would make its strong 1024 bit encryption and security vulnerable: "We could do it but only if we re-engineered the way it works and we don't have the time right now."—Niklas Zennstrom, co-founder of Skype, on the Skype security model[4]
The canonical Skype architecture and security model are described in detail in a book entitled, Skype: The Definitive Guide[5] from Que Publishing. In addition, at least two analyses of the Skype code have been published. Tom Berson of Anagram Laboratories, an encryption and security specialist of over thirty years standing, was invited by Skype to analyse their source code in October 2005. Separately, a reverse-engineered study by Philippe Biondi and Fabrice Desclaux, of the actual Skype release package in action, was presented at BlackHat Europe in March 2006.[6][7]
The conclusions of the two analyzes were as follows:
- There are two sets of issues—discussion of the Skype system in general, and review of the security within its various parts and communications.
- Skype is a "complete black box"—that is, it is extremely hard for the lay user to identify what it is doing, or what it might be doing, or how appropriately it is doing it. It uses security through obscurity to make itself troublesome to analyse or reverse engineer without a significant amount of work, or use of emulation.
- Searches for contacts, and connection via supernodes, are trusted instead of requiring authentication: There are notable "holes" in security in the area of the global Skype network—in some areas, "Skype trusts any computer that speaks Skype".
- The Skype software itself uses a great deal of code obfuscation and decryption in memory, including hundreds of checksummers and other anti-reverse-engineering devices.
- The company claims that the protocol includes 1536- and 2048-bit public/private key pairs. These are not considered excessively long by modern standards, but are a strong barrier to decryption. Apparently, users of paid services obtain a replacement 2048 bit key (the 1536 bit key being standard). It also uses 256-bit AES over 128-bit blocks, which is considered strong.
- The Skype system automatically selects certain users with fast CPUs, good broadband connections and no firewall issues to be either "supernodes" or "relays", through which other users may connect. Skype can therefore utilise other users' bandwidth. (Although this is allowed for in the EULA, there is no way to tell how much bandwidth is being used in this manner). There are some 20,000 supernodes out of many millions of users logged on. Skype Guide for network administrators [5] claims that supernodes carry only control traffic up to 5 kbytes/s and relays may carry other user data traffic up to 10 kbytes/s (for one video call). A relay should not normally handle more than one "relayed connection".
- Every package virtually, including the actual software itself, is encrypted, often by means of public/private key signing methods or AES.
- Skype's file-transfer function does not contain any programmatic interfaces to antivirus products, although Skype claims to have tested its product against antivirus "Shield" products. If the EICAR test file is sent over Skype's file-transfer service, every major antivirus product appears to catch the virus and halt its transmission or reception via Skype.
- The lack of clarity as to content means that firewalls and systems administrators cannot be sure what Skype is doing. (The combination of an invited and a reverse-engineered study taken together suggest Skype is not doing anything hostile.) Firewall rules for Ip tables were given to block Skype for corporates.
- The full functionality of Skype was not reviewed; both studies appear to have focused upon its security. Thus, it cannot be said what else may or may not be present.
- The actual communication of any given Skype conversation is reported to appear relatively secure; both cryptographic analyses concluded that Skype had made good use of modern encryption techniques and had coded the actual encryption algorithms correctly within the software.
[edit] Resource usage
Skype accesses the hard disk several times per minute. This can be verified by observing the HDD's activity LED, or by using a file access monitor such as FileMon.[8] Although those accesses are small, extremely fast, and safe in the short term, they can be harmful in the long term. In particular, the continuous access pattern does not allow the disk to enter "sleep" or "idle" modes while Skype is active, even when offline. This will cause the computer to consume more energy than otherwise, even when idle, but will not affect the lifespan of the HD (a hard disk will actually last longer if left spun up compared to being constantly spun up and down. Spinning down a hard disk is strictly a power-saving feature). Stronger HDD caching does not seem to improve this behavior.
Also, as mentioned above, certain users are selected by software to act as "supernodes". Under certain conditions, Skype is reportedly willing to accept thousands of connections, but is stated to limit itself to 40Kb/s upload and download.[9][10][11]
[edit] Confidentiality of data
Since a Skype connection may be routed through an intermediate peer, 256-bit AES encryption actively encodes the data stream of each call, or file transfer. Skype uses 1024-bit RSA keys to secure the pairwise negotiation of an AES symmetric session key over an untrusted channel (cf. http://www.skype.com/help/faq/privacy.html). Skype claims that the proprietary session establishment protocol is efficient and prevents both man-in-the-middle and replay attacks. The software is not self-certifying which means it needs to connect and login to a centralized Skype server to certify each user's public key.
One possible interception scenario would be for Skype to route a connection via a specific intermediate peer, which may also be provided with copies of the keys. This would enable law enforcement authorities to intercept calls with the cooperation of the Skype company. This Skype-sanctioned man-in-the-middle technique would be impossible for an end-user to detect.
Skype currently permits multiple concurrent logins: if an attacker is able to obtain a user's login password, the attacker could login as that user, and change their status to "Hidden". Thereafter, any chat sessions involving the real user are copied to the hacker's "ghost" account. If a user keeps their password secure, this is not of concern.
[edit] Integrity/authenticity of data
The integrity of the data, i.e. data modified while traveling though peers, even if encrypted, is unknown and undocumented. The mechanism and implementation has been examined in Berson's report (referenced below).
[edit] Authenticity of user identity
Skype provides an uncontrolled registration system for users: registration requires no proof (in means of state-issued ID card) of the identity of the user. This works two ways: you can use the system safely without revealing your real-life identity to other users of the system, but on the other hand you have no guarantees that the person you communicate with is the one they say they are in real life. The downside of this is that it is easy to use the personal name (but not identity) of a trusted person as a Skype nickname and trick a naive user into revealing information or executing a program sent to them.
It should be noted that this behavior is common to all digitally provided services: the exception is certificates from trusted certificate authorities with all the known drawbacks.
[edit] Traffic analysis
Skype incorporates some features which obfuscate its traffic, but it is not specifically designed to thwart traffic analysis and therefore does not provide anonymous communication. Some researchers have also been able to watermark the traffic so that it is identifiable even after passing it through an anonymizing network [6]. Even short skypeout calls have been traced, leading to the apprehension of at least one suspect.
[edit] Milestones and releases
- For detailed changelog see Skype changelog.
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Versions now exist for Microsoft Windows (2000, XP and CE (Pocket PC)), Mac OS X and GNU/Linux. The Linux version runs on FreeBSD through its Linux binary compatibility.
[edit] Usage
It was reported that eight million concurrent Skype users were online as of November 8, 2006.[25]
| Date[26] | Users online | Days |
|---|---|---|
| 2006-11-08 | 8,000,000 | 71 |
| 2006-08-29 | 7,000,000 | 155 |
| 2006-03-27 | 6,000,000 | 66 |
| 2006-01-20 | 5,000,000 | 92 |
| 2005-10-20 | 4,000,000 | 155 |
| 2005-05-18 | 3,000,000 | 93 |
| 2005-02-14 | 2,000,000 | 117 |
| 2004-10-20 | 1,000,000 | 418 |
| 2003-08-29 | 0 | - |
SR Consulting reviewed 4 million Skype user profiles in October 2005 and produced some demographic information reported by Skype News[27] and Skype Journal.[28]
- Average claimed age: 29.7 years old.
- About 46% of Skypers are in Europe, but Brazil and China have the most Skype users of any country, with China coming in at 13% of the Skype population.[29]
- Gender information is inconclusive so far. More than half of all users declined to state their sex.
[edit] Traffic volume
Although the volume of international traffic routed via Skype is significant, the quantity is still small when compared to a global switched and VoIP traffic base of 264 billion minutes. Computer-to-computer traffic between Skype users in 2005 was equivalent to 2.9% of international carrier traffic in 2005 and approximately 4.4% of total international traffic in 2006[30].
[edit] Features
[edit] SkypeOut
SkypeOut allows Skype users to call traditional telephone numbers, including mobile telephones, for a fee. This fee is as low as USD$0.024 per minute for most developed countries, and as high as USD$2.142 per minute for calls to the dependency of Diego Garcia. After 180 days of not making a SkypeOut call the Skype balance expires. This policy makes Skypeout a poor service for infrequent users as they will often lose their entire account balance.
Currently, SkypeOut calls within the USA and Canada to destinations within USA and Canada are free.[7]
SkypeOut calls to toll free numbers in France (+33 800, +33 805, +33 809) , Poland: (+48 800) , UK: (+44 500, +44 800, +44 808 ) and the USA and Canada: (+1 800, +1 866, +1 877, +1 888 ) are free for all Skype users, even if they do not have the SkypeOut service. [8]. SkypeOut calls to toll-free numbers in Belgium (+32 800) do not work.
[edit] SkypeIn
SkypeIn allows Skype users to receive calls on their computers dialed by regular phone subscribers to regular phone numbers. Permits users to subscribe to numbers in Australia, Brazil, Denmark, Estonia, Finland, France, Germany, Hong Kong, Japan, Poland, Sweden, Switzerland, UK and USA.
For example, a user in San Francisco could create a local telephone number in Helsinki. Callers from Helsinki would pay only local rates to call that number.
[edit] Skype voicemail
Skype Voicemail was released on March 10, 2005. This service allows callers to leave voice-mail messages for Skype users who are indisposed.
Skype Voicemail has experienced numerous problems over the past year and users complain that many voice mail calls are never received. Additionally, the SkypeIn service occasionally fails to record certain incoming calls on the program's history page. These problems have not been completely resolved.
[edit] Skype chat
Skype supports group text chat with an interface similar to IRC with 100 People.
The Macintosh version uses the same message view style format as Adium, though with a different filename extension. Message view styles made for Adium can be installed for Skype, and they do not even need to be renamed.[31] There are a couple of cosmetic bugs,[32] but ignoring those, Adium styles work without modification. This feature is not present in the Windows, Linux, and Pocket PC versions of Skype.
[edit] Skype video calling
On Windows XP (Windows 2000 users require DirectX 9.0 for video calls) and Mac, Skype 2.0 (and above) supports videoconferencing, making Skype one of the few cross-platform video conferencing solutions between Windows and Mac. Skype only supports one-to-one video chat.
[edit] Skypecasts
Skypecasts was released on May 3, 2006. Skypecasts are live, moderated conversations allowing groups of up to 100 people to converse, moderated by the �host� who is able to mute, eject or pass the virtual microphone to participants when they wish to speak. Skypecasts do not support chat windows to share text information (such as URLs) with participants.
[edit] Skype SMS
One of the few new features in Skype 2.5.0.72 beta is the ability to send SMS messages to mobile phone numbers (a feature commonly used in other IM software such as ICQ, AOL Instant Messenger, Yahoo Messenger and Windows Live Messenger).
[edit] Skype web toolbar
The Skype Web Toolbar recognizes phone numbers and Skype Skype. Currently only available for Internet Explorer and Mozilla Firefox on Windows. There is also a toolbar for ThunderBird.
[edit] Skype Zones
Skype Zones Beta is software powered by Boingo that provides access to Skype through Skype-friendly hot spots.
[edit] Skype history logs
Skype Zones Beta is software that allows users to keep track of their conversations. A log file is created for each contact on a user's contact list. Log files are stored locally, meaning they are not available if a user switches computers. By default, the option to log conversations is disabled, but can be enabled in the tools / privacy panel.
[edit] Skype Hardware
Recently a number of manufactures have launched hardware devices compatible with Skype. These are usually either tethered to a PC, or have a built-in Wi-Fi client to allow calling from Wi-Fi hotspots like the Netgear SPH101 Skype Wi-Fi Phone.
[edit] Additional Tools
Skype Beta version 3.0 provides additional tools under "Do More" Submenu. Tools added includes,Pamela Voice recorder for recording voice calls and many games.
[edit] Criticisms
Skype has been criticised over its use of a proprietary protocol, instead of an open standard like H.323, IAX, or SIP, since this makes it impossible for other providers to interact with the Skype network. There are of course clear business reasons for this, since it helps protect the SkypeOut revenue stream from competition.
A design limitation of Skype is that, if given access to an unrestricted network connection, Skype clients can become supernodes. These supernodes hold together the peer-peer network and provide data routing for those behind restrictive firewalls. Unfortunately, these supernodes can generate a significant amount of bandwidth. For this reason some network providers, such as universities, have banned Skype.[citation needed]
A third party paper analyzing the security and methodology of Skype was presented at Black Hat Europe 2006.[33] It analyzed Skype and found these things:
- Heavy use of anti debugging techniques (used to deter development of alternative clients, hacking tools)
- Heavy use of obfuscation of code (slows reverse engineering, less description of what program code does internal to the executable file)
- Keeps chatting on the network, even when idle (even for non-supernodes. may be used for NAT traversal)
- Blind trust in anything else speaking Skype
- Ability to build a parallel Skype network
- Lack of privacy (Skype has the keys to decrypt sessions)
- Heap overflow in Skype
- Skype makes it hard to enforce a (corporate) security policy
- "No way to know if there is/will be a backdoor"
Another criticism of Skype has been content filtering. See: Internet censorship in the People's Republic of China.
While available for most operating systems, there is no Skype version for the Palm OS which is widely used in mobile devices like the Treo 700p.
Skype has been heavily criticized in the Linux community for bugs and delays in the Linux version [9].
[edit] Legal and political aspects
Skype faces challenges from two main legal and political directions - challenges to its intellectual property, and political concerns by governments who wish to exert more formal control over aspects of their telecommunications systems.
Skype's technology is proprietary and closed to outside review. It is unknown to what extent it can potentially intrude upon other parties' patents and copyrights. It is not unreasonable, therefore, to expect legal challenges from third parties concerning Intellectual Property issues.
[edit] Legal challenges
[edit] Streamcast lawsuit
In January, 2006, StreamCast Networks filed a complaint in U.S. District Court in Los Angeles, accusing Skype of stealing its peer-to-peer technology. The $4.1 billion lawsuit did not initially name eBay, Skype's parent company; however, the lawsuit was amended in a filing with Federal Court in the Central District of California on May 22, 2006, to include eBay and 21 other parties as defendants.
Streamcast seeks a worldwide injunction on the sale and marketing of eBay's Skype Internet voice communication products, as well as billions of dollars in unspecified damages.
[edit] IDT lawsuit
On June 1, 2006, Net2Phone (the Internet telephone unit of IDT Corp.) filed a lawsuit against eBay and Skype accusing the unit of infringing US Patent 6,108,704[34] which was granted in 2000.[35]
[edit] Political issues
[edit] China 2005
For a brief period, SkypeOut was blocked in some regions of mainland China (notably Shenzhen) by the operator China Telecom for undisclosed reasons; it has been speculated that this may relate to SkypeOut's ability to take lucrative international and long-distance business away from the People's Republic of China's state-controlled telecommunications companies.
Skype is one of many companies (others include AOL, Google, Microsoft, Yahoo, Cisco) which have cooperated with the Chinese government in implementing a system of Internet censorship in mainland China. Critics of such policies argue that it is wrong for companies to assist in such policies, which might allow them to profit from censorship and restrictions on freedom of the press and freedom of speech. Human rights advocates such as Human Rights Watch and media groups such as Reporters Without Borders state that in their view, if companies stopped contributing to the authorities' censorship efforts the government could be forced to change.[36]
Niklas Zennstrom, chief executive to Skype, told reporters that its joint venture partner in China is operating in compliance with domestic law. "Tom Online had implemented a text filter, which is what everyone else in that market is doing," said Mr Zennstrom. "Those are the regulations." "I may like or not like the laws and regulations to operate businesses in the UK or Germany or the US, but if I do business there I choose to comply with those laws and regulations. I can try to lobby to change them, but I need to comply with them. China in that way is not different."
[edit] France 2006
In September 2005, the French Ministry of Research, acting on advice from the general secretariat of national defence, issued an official disapproval of the use of Skype in public research and higher education; some services are interpreting this decision as an outright ban. The exact reasons for the decision were not given, but speculatively may relate to issues noted earlier, relating to inability to monitor the nature of information being communicated, possible extreme resource usage, or unknown potential actions of the software.
[edit] India 2006
In December 2006, the Indian Government announced they are preparing a crackdown on VoIP services, citing security risks and loss of revenue. The clampdown is targeted at outsourcers and other Indian IT businesses that use foreign owned VoIP services, such as Skype and Yahoo!, to cut their phone bills and evade the six percent revenue share and 12 percent tax imposed on local services by the government. According to the The India Times, companies must reveal the names of authorised service providers they purchase bandwidth and internet telephony minutes from. Companies will also have to promise that they will not use the services of unlicensed foreign providers.
[edit] Skype group (corporate)
On October 14, 2005, eBay acquired the company for ¬1.9 billion in cash and stock, plus an additional ¬1.5 billion in rewards (earn out) if goals are met by 2008.[37][38]
[edit] Competition and alternatives
[edit] Open source alternatives
- Kiax: VoIP application based on IAX
- PSI: The current Beta version has protocol support for Google Talk
- Switchboard: Free VoIP applet which works from within a web browser. Works on Windows, Mac, Linux, and any other Java enabled platform. No installation necessary
- Tapioca: Includes support for Google Talk
- WengoPhone: A free VoIP application based on SIP open standard
- Ekiga: A free application that supports both H.323, SIP, audio and video. Ekiga was formerly known as GnomeMeeting. So far works only with various Linux based systems. No version for Microsoft Windows has been released yet, but there is a working snapshot available.
[edit] Closed source alternatives
- amiciPhone: A secure peer-to-peer VoIP application
- Google Talk: A popular service provided by Google
- Gizmo Project: A closed source VoIP application based on SIP open standard and uses SRTP between clients. Now offering free landline/cell calls to over 60 countries
- iCall: A closed source free VoIP application based on SIP open standard and providing free PC to Phone calling in the US and Canada.
- Jajah: Alternative where no headset, no download, no installation and no broadband connection is necessary. A VoIP call gets activated between two normal phones.
- Secure Shuttle Transport (SST): Free encryption and secure messaging software including VoIP and video. Works on PCs running Windows 98 or higher.
- Raketu: A VoIP service that combines communication, information, and entertainment. Its integrated multi-messenger allows communication with contacts from AOL Instant Messenger, ICQ, MSN Messenger, Google Talk, Yahoo Messenger and Skype.
- SightSpeed: Free video and voice calling service supporting Mac & Windows. Also allows phone out and in calling.
- Parlino: A VoIP network based on open standard SIP-protocols, launched by Parlino S.A.
- Vbuzzer: A VoIP softphone and service as well as an active advocator of SIP open standard
- VoipBuster: A VoIP application offering 300 minutes per week of free calls to landlines in many countries, including the EU, USA, Australia, etc.
- VoipStunt: A VoIP application offering 300 minutes per week of free calls to landlines in many countries, including the EU, USA, Australia, etc.
- Zfone: A solution of Phil Zimmermann (inventor of PGP) to encrypt VoIP (SIP) sessions, protocol published as IETF draft. [10]
- TipicIM: A free VoIP application, Videocalling based on XMPP/Jabber and Speex audio codec support
- [ClosedTalk]®: A secure VoIP software free from CE-Infosys for Business/Personal use. Works on PCs running Windows 2000/XP. [ClosedTalk]" exposes �man in the middle� attacks by displaying a short security message on both caller screens for comparison.
- BT Communicator: A VoIP service from British Telecom (BT plc.)
[edit] See also
- Skype Protocol
- Presence information
- Voice over IP
- Instant messaging
- Videoconferencing
- Secure communication
- Skype Journal: An independent online magazine about Skype
- Horizon Global
- Nuvvo eLearning Service: an on-demand service with SkypeWeb Presence integration
[edit] References
- ^ Jaanus Kase. Skype is expanding engineering to Prague. Skype Blogs. Retrieved on 2006-12-05.
- ^ Interview with Jaanus Kase from Skype. KDE News. Retrieved on 2006-06-13.
- ^ Skype Privacy FAQ. Skype. Retrieved on 2006-12-05.
- ^ "VoIP suffers identity crisis", The Register, June 15, 2004.
- ^ Harry Max. Skype: The Definitive Guide. Retrieved on 2006-08-22.
- ^ Tom Berson. Skype Security Evaluation (PDF). Retrieved on 2006-06-13.
- ^ Biondi and Desclaux. Sliver Needle in the Skype (PDF). Retrieved on 2006-06-13.
- ^ FileMon for Windows. Sysinternals. Retrieved on 2006-06-17.
- ^ Bruno Giussani. Swiss magazine digs deeper in social blog. Lunch over IP. Retrieved on 2006-06-17.
- ^ Fear of a Skype Planet. Paul Kedrosky. Retrieved on 2006-06-17.
- ^ Skype supernodes sap bandwidth. Computerworld. IDG. Retrieved on 2006-06-17.
- ^ Jack McCarthy. China bans Skype. InfoWorld. Retrieved on 2006-06-17.
- ^ eBay Completes Acquisition of Skype. eBay. Retrieved on 2006-06-17.
- ^ Skype Launches Next Generation Free Internet and Video Calling for Everyone. Skype. Retrieved on 2006-06-17.
- ^ Philippe BIONDI and Fabrice DESCLAUX. Silver Needle in the Skype. blackhat. Retrieved on 2006-03-02.
- ^ Bambi Francisco. eBay execs say Skype growing fast. MarketWatch. Retrieved on 2006-06-17.
- ^ Free calls to all landlines and mobile phones within the US and Canada. Skype. Retrieved on 2006-06-17.
- ^ [1]
- ^ [2]
- ^ [3]
- ^ Skype launches free SkypeOut calls within France
- ^ 8.000.000 online!
- ^ Introducing Skype 3.0 Beta for Windows
- ^ [4]
- ^ Jaanus. Eight million online. Skype Blogs. Retrieved on 2006-11-08.
- ^ 8 million onliners. skypenumerology. Retrieved on 2006-11-08.
- ^ Mathaba.net Who is using Skype?. Skype News. Retrieved on 2006-06-17.
- ^ What do people put in their Skype profiles?. Skype Journal. Retrieved on 2006-06-17.
- ^ "Executives say China is Skype's biggest market", China View, Xinhua News Agency, May 5, 2006.
- ^ International carriers' traffic grows despite Skype popularity. TeleGeography Report and Database. Retrieved on 2006-12-07.
- ^ Adding chat styles to Skype. blodspot.com. Retrieved on 2006-06-13.
- ^ Adium message styles and Skype (1 updates). Soeren Says. Retrieved on 2006-06-13.
- ^ Philippe BIONDI and Fabrice DESCLAUX. Silver Needle in the Skype. blackhat. Retrieved on 2006-03-02.
- ^ Skype Patent 6108704. US Patent Office. Retrieved on 2006-06-17.
- ^ Pallavi Gogoi. "Skype Under Attack", Business Week, McGraw Hill, June 6, 2006.
- ^ Skype uses peer-pressure defense to explain China text censorship. The Register. Retrieved on 2006-06-18.
- ^ eBay Completes Acquisition of Skype. Skype. Retrieved on 2006-06-12.
- ^ "eBay to buy Skype in $2.6bn deal", BBC, September 12, 2005.
[edit] External links
- Official Skype website
- Scientific Research on Skype (Reverese Engineering, etc.)
- White paper on Skype, focus on supernodes
- Skype Security Evaluation by Tom Berson (Anagram Laboratories)
- Graze the page of Skype
- Paper discussing Skype's internals from a security perspective (Black Hat Europe 2006) - Philippe Biondi & Fabrice Desclaux
- Skype, Zennstrom, Friis Et Al Sued for RICO Violations
- Kodak Photo Voice for Skype
- Skype to Charge for Unlimited Phone Call Plan
Categories: Cleanup from November 2006 | All pages needing cleanup | Articles with unsourced statements | Telephony | VoIP software | Free VoIP software | File sharing programs | Teleconferencing | Groupware | Communication | Collaboration | Instant messaging | Online social networking | On-line chat | Telephone service enhanced features | Freeware | Windows instant messaging clients | Mac OS X instant messengers | Linux instant messaging clients | Web 2.0 | EBay
