"We are sorry for the inconvenience," Paulen added.
AVG did not publicize the problem on the front page of its Web site and did not immediately respond to several questions, including how the flawed signature slipped through internal checks.
This wasn't the first time that AVG has been in the spotlight. Last summer, the LinkScanner Search-Shield component of its antivirus software triggered a flood of bogus traffic to Web sites, angering site operators.
Nor is AVG the only security vendor to issue a damaging update. Only last September, a Trend Micro signature mistook several critical Windows XP and Vista system files for malware, blocking the PCs from booting.