Blizzard Downloader

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Blizzard Downloader

v1.5 (19) downloading The Burning Crusade Blizzcon trailer
Developer:	Blizzard Entertainment
Latest release:	1.6 (39) /
OS:	Mac OS X, Microsoft Windows
Use:	BitTorrent client
Website:	World of Warcraft.com

Blizzard Downloader or Background Downloader is a BitTorrent client used in Blizzard Entertainment's MMORPG World of Warcraft. It is used to download large updates for the game, smaller updates being downloaded directly from the server. Early versions were based on the source code of the original BitTorrent client, though it is unclear what the source model is now. When a large update is issued a Blizzard Downloader is downloaded to the WoW directory and it fetches the update file, using the standard ports 3724 and 6881. BNUpdate then applies the patch. Blizzard offers an individual client for each download they offer, instead of just a torrent file. The Blizzard downloader also runs in the background under the name of "Background Downloader" while World of Warcraft is open, This program uploads files to newcomers who need patches.

1 Structure
- 1.1 Macintosh version
- 1.2 Windows version
2 Exploits
3 See also
4 External links

[edit] Structure

[edit] Macintosh version

The Blizzard Downloader bundle is actually a plain BitTorrent client that has a .torrent file inside. The .torrent can be opened by other BitTorrent clients giving the user greater control over how the download is handled.

/Applications/World of Warcraft/WoW-old-to-new-local-downloader.app/Contents/
- MacOS/
  - Blizzard Downloader - executable file
- Resources/
  - downloader.torrent - torrent file

Note: GUI & localization files not listed for readability.

[edit] Windows version

It is possible to extract the .torrent file from the end of the downloader executable:

Search for d8:announce at the end of the downloader executable, and then save from this point to the end of the executable to a separate file. Add .torrent to the file name and open in any BitTorrent Client.

Earlier versions included a Macintosh-variant of the .torrent as well, but this has been removed in later versions. You may also need to remove some trailing characters at the end of the file, since they do not all belong to the .torrent; essentially, the resulting file has to be Bencode-compliant.

Alternatively, start the background downloader and check the end of Logs\BackgroundDownload.log for a message like this:

Creating cache file C:\Program Files\World of Warcraft\Cache\BackgroundDownload.torrent

This .torrent file can be used with any BitTorrent client. Alternate locations may include the Cache folder, depending on the WoW client's locality.

[edit] Exploits

This article documents a current event.
Information may change rapidly as the event progresses.

Like other Bittorrent clients, it is possible to exploit the Blizzard downloader by infecting parts of the update files with virus code. The entire swarm will then unwittingly distribute the infected file, as it's impossible for a Bittorrent client to tell an infected file from an uninfected one. This was done during the 2.0.1 patch, and the trojan which was distributed damaged or disabled many users' (possibly as many as tens of thousands) copies of the game.