Kaspersky sent out a buggy signature update Monday night that largely paralyzed countless computers running XP. The bug apparently made web protection so strict that the Kaspersky products quietly blocked almost all internal and external network connection attempts. The virus scanner also pushed CPU utilization to 100 per cent as soon as a user opened a browser.

The company did release a fixed update just two hours later – but that wasn't particularly helpful for the computers that couldn't download it because of the strict blocking. It seems users weren't completely cut off, though, with many saying that they could still load Google and Yahoo.

Apparently all XP computers with Kaspersky security products were affected across the board. Both Kaspersky Endpoint Security 8 administrators and users of Kaspersky Internet Security 2013 reported the bug on the company's support forum. Computers with Windows 8, 7 and Vista were not affected.

For enterprise solutions, temporary fixes included deactivating web protection with a security policy defining exceptions for the relevant external ports. Home users were also able to restore their internet connection by deactivating web protection.

Kaspersky support advised administrators to first disable the Web AV component, then completely empty out the central update repository and download the updated virus signatures, although this process could take several hours. For private PCs, turning off web protection before manually starting the update function was apparently sufficient.