August 7, 2015 10:49 AM EDT

If you use Firefox, you could be at risk because of a flaw in the software that could be used to steal files from your computer.

In a blog post published Thursday, Mozilla explained: “A Firefox user informed us that an advertisement on a news site in Russia was serving a Firefox exploit that searched for sensitive files and uploaded them to a server that appears to be in Ukraine.”

“The vulnerability comes from the interaction of the mechanism that enforces JavaScript context separation (the “same origin policy”) and Firefox’s PDF Viewer,” Mozilla said. “Products that don’t contain the PDF Viewer, such as Firefox for Android, are not vulnerable,” the post continued.

Not to worry though, as Mozilla has already released an update to fix the problem.

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