Attention, Firefox users: Stop what you’re doing and update your web browser.
An exploit discovered on Wednesday could potentially search your local files and upload them to a server that appears to be in Ukraine, according to a blog post Mozilla published on Thursday. The company strongly recommends users update to the Firefox 39.0.3 or Firefox ESR (Extended Support Release) 38.1.1.
An advertisement on an unnamed Russian general news website can use a security vulnerability to perform the search and upload without leaving any trace on your computer, according to the post.
The security bug affects Windows and Linux users; Mac users are reportedly safe, though “would not be immune,” according to the post by Mozilla lead security expert Daniel Veditz.
Veditz added that users who have ad-blocking software enabled may be unaffected.