Two experimental add-ons, Version 4.0 of Sothink Web Video Downloader and all versions of Master Filer were found to contain Trojan code aimed at Windows users. Version 4.0 of Sothink Web Video Downloader contained Win32.LdPinch.gen, and Master Filer contained Win32.Bifrose.32.Bifrose Trojan.
This vulnerability is known to affect Firefox on Windows only, if either Master Filer or Version 4.0 of Sothink Web Video Downloader are installed. Versions of Sothink Web Video Downloader greater than 4.0 are not infected. Master Filer was downloaded approximately 600 times between September 2009 and January 2010. Version 4.0 of Sothink Web Video Downloader was downloaded approximately 4,000 times between February 2008 and May 2008. Master Filer was removed from AMO on January 25, 2010 and Version 4.0 of Sothink Web Video Downloader was removed from AMO on February 2, 2010. AMO performs a malware check on all add-ons uploaded to the site, and blocks add-ons that are detected as such. This scanning tool failed to detect the Trojan in Master Filer. Two additional malware detection tools have been added to the validation chain and all add-ons were rescanned, which revealed the additional Trojan in Version 4.0 of Sothink Web Video Downloader. No other instances of malware have been discovered.
This issue was originally reported by CatThief.
Here is a list of antivirus programs known to detect the trojans found in the affected add-ons.