“Everyone who downloaded the most recent Vietnamese language pack since February 18, 2008 got an infected copy.  While we cannot determine the exact number of compromised downloads, there have been 16,667 total downloads of the Vietnamese language pack since November 2007, so we anticipate the impact on users to be limited,” reads the official statement.

It all started with a report from a user, claiming that the pack had been found to include the Xorer Trojane. The Firefox maker  confirmed the news.

According to Mozilla, it’s most likely that the  mishap was the result of a developer’s system getting infected. Whatever the case may be, one thing is certain: Firefox users got a taste of unwanted ads.

The Firefox 2 Vietnamese language pack has now been pulled from the downloads list and will be added shortly after a thorough clean up. Until then, users are advised to disable this package using the add-ons dialogue on the Tools menu.

Mozilla stated that this was the first incident of its kind to affect Firefox and promised to revamp its testing procedure.