An update from AVG on Wednesday night rendered 64 bit Windows 7 systems unstable after it was applied.
Several Register readers have been affected by the problem, which leaves machines in a continuous reboot loop.
AVG has pulled the problem update (3292) and published an advisory apologising for the cock-up and providing instructions on how to get hobbled systems back up and running again.
Recovering a Blue Screened PC is more involved than simply rebooting in safe mode, as the security vendor explains. Desktop versions of Windows 7 seem particularly prone to the bug.
It's unclear whether or not other versions of Windows are vulnerable to going weak at the knees after applying the misfiring update from AVG. Both free and paid-for versions of the software seem to be problematic.