Four browser extensions from Avast and AVG (Avast Online Security, AVG Online Security, Avast SafePrice and AVG SafePrice) have been taken down from Firefox. It has been recently discovered that those extensions, usually automatically installed together with Avast and AVG products, have been collecting much more data on the users that they are intended to.
The extensions are meant to warn users against dangerous websites and help online shoppers. The data gathered through those extensions include full URL of visited websites, a unique user identifier, page title, referrer URL, OS version, country code, the exact browser version, and more. All the data together allows precise reconstruction of the user's browsing behaviour: how many tabs they have open, what websites they visit and when, how much time they spend reading/watching the contents, what they click there and when they switch to another tab.
Although Google has also been notified, the extensions are still available on the Google Chrome Web Store. Therefore, all Chrome users are advised to disable or remove them if they have ever used Avast/AVG products.