Ad filtering or ad blocking is removing or altering advertising content in a webpage. Advertising can exist in a variety of forms including pictures, animations, text, or pop-up windows. More advanced filters allow fine-grained control of advertisements through features such as blacklists, whitelists, and regular expression filters. Certain security features also have the effect of disabling some ads.
The benefits include quicker loading and cleaner looking Web pages free from advertisements, lower resource waste (bandwidth, CPU, memory, etc.), and privacy benefits gained through the exclusion of the tracking and profiling systems of ad delivery platforms.
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One consequence is decreased revenue to the website that was sustained by advertisements.[1]
Almost all modern web browsers include a pop-up blocker. Opera, Konqueror, Maxthon 2, and Internet Explorer 8[1] also include content filtering, which prevents external files such as images or JavaScript files from loading. Content filtering can be added to Mozilla Firefox and related browsers with Adblock Plus, and a number of sources provide regularly updated filter lists. For Internet Explorer there are several add-ons available like Simple Adblock, IE7Pro, Adblock Pro and Quero that also allows users to temporarily unblock blocked content. A rudimentary content blocking feature is integrated in Opera and does not require an add-on. For Google Chrome, which has had extensions available since v2.0, the AdSweep and FlashBlock extensions are available, as well as AdBlock Plus and AdBlockforChrome. Another method for filtering advertisements uses CSS rules to hide specific HTML and XHTML elements.
A number of external applications offer ad filtering as a primary or additional feature. A traditional solution is to customize an HTTP proxy (or web proxy) to filter content. These programs work by caching and filtering content before it is displayed in a user's browser. This provides an opportunity to remove not only ads but also content which may be offensive, inappropriate, or simply junk. Popular proxy software which blocks content effectively include Privoxy, Squid, Proximodo, Adextinguisher, Ad Muncher, Death 2 Ads, Guidescope and Proxomitron. The main advantage of the method is freedom from implementation limitations (browser, working techniques) and centralization of control (the proxy can be used by many users). The major drawback is that the proxy sees only raw content and thus it's difficult to handle JavaScript-generated content.
Further information: hosts file.
This method exploits the fact that most operating systems store a file with IP address, domain name pairs which is consulted by most browsers before using a DNS server to look up a domain name. By assigning the local 127.0.0.1 IP number to each known Ad server, the user directs traffic intended to reach each Ad server to the local machine. Running a suitable web server locally the ad content can be replaced with anything the user wishes.
Advertising can be blocked by using a DNS server which is configured to block access to domains or hostnames which are known to serve ads. Examples are AdBarricade, DNS Redirector, DNSKong and OpenDNS[2].