Problems with antivirus updates from Trend Micro left some users with unusable computers late last week.
The signature update, pushed out on Friday morning, incorrectly identified key Windows system files as being infected with a Trojan. The security software quarantined these important files leaving users with unstable systems. Trend later fixed the problem by issuing updated signature definition files that avoided the false positive.
For affected users that was far from the end of their worries. They were still left with the hassle of repairing Windows and (perhaps) reinstalling their security software.
Consumers were hardest hit by the glitch, which affected users of Trend Micro Internet Security, Trend Micro Internet Security Pro and Trend Micro AntiVirus. In an advisory to customers forwarded to The Register, Trend Micro said that a small number of consumers were hit by the snag and explained that the faulty update "inaccurately identified certain files as malicious and quarantined them". It admitted that this might cause system instability.
In response to queries from El Reg, prompted by reader emails, Trend Micro issued a statement:
On 5th September 2008 at 02h00 GMT, a false alarm was triggered in Trend Micro Internet Security caused by a new pattern file that had been issued. Specifically the inclusion of pattern Troj_Generic.ADV issued within Official Pattern Release (OPR) version 5.525.50 quarantined several Microsoft Windows DLLs.
In mitigation we removed the detections in question and at 12h15 GMT on 5th September, OPR 5.527.50 was released that resolved this issue. Customers who downloaded OPR 5.525.50 needed only to update to the latest OPR. All other customers who updated thereafter received the latest OPR.