A signature update was released yesterday by Kaspersky Lab. The problem is that it misdiagnoses Windows Explorer as a file with a virus.

Many people were affected and some of them had set their anti-virus software to auto-delete infected files so that one of the core Windows component was deleted which is explorer.exe.

One person reported, “A false positive caused the deletion of explorer.exe. It would have only caused problems for companies performing their network scan during the hours that the dodgy update was present - which included me, unfortunately. I was working out of hours to fix the previous Kaspersky update problem. I finally finished sorting it all at 5am.”

Source: Channel Register