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Mozilla yesterday posted a notice on its AMO blog (that’s an acronym for their add-on site that two add-ons have been found infected with Trojan code: Sothink Web Video Downloader v. 4.0 and all versions of Master Filer.

Version 4.0 of Sothink Web Video Downloader contained Win32.LdPinch.gen and Master Filer contained Win32.Bifrose. According to the blog, Masterfiler was downloaded 600 times before it was removed from the site Jan. 25 and Sothink was downloaded more than 4,000 times before it was removed Feb. 2.

Mozilla said “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.”

Blog post here.

Update 02/10:

It turns out that the Sothink Video Downloader 4.0 was NOT infected. It was tagged as malicious because of a false positive in the scanner that Mozilla used at the time.

Mozilla posted the following yesterday:

“Since that disclosure, we’ve worked with security experts and add-on developers to determine that the suspected trojan in Version 4.0 of Sothink Video Downloader was a false positive and the extension does not include malware. The same investigation also confirmed that the Master Filer extension included a valid instance of a trojan. Our estimate of 6,000 affected downloads has been revised to under 700. The Sothink Video Downloader has been re-enabled on AMO.”

Mozilla’s update here.

Tom Kelchner