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McAfee false positive bricks enterprise PCs worldwide

World of hurt

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Enterprise customers of a widely used McAfee anti-virus product were in a world of hurt on Wednesday after an update caused large swaths of their machines to become completely inoperable.

The problem started around 2 pm GMT when McAfee pushed out DAT 5958 to users of VirusScan Enterprise. The virus definition falsely identifies a core Windows file as infected, quarantines it and then shuts down the machine. When restarted, the PCs are unable to load Windows, a glitch that mires them in an endless reboot cycle.

"We support customers' platforms, and it means we are currently unable to do that," said the head of infrastructure security for a worldwide IT firm who asked not to be identified because he's not authorized to speak to the press. "Basically, our engineers are currently unable to work."

In a statement, McAfee said the false positive "can result in moderate to significant performance issues" on machines running Windows XP service pack 3, and that the defective definition has been removed from download servers. The infrastructure security head said XP machines running SP 1 and SP 2 were also affected.

"McAfee teams are working with the highest priority to support impacted customers and plan to provide an update virus definition file shortly," the statement continued. "McAfee apologizes for any inconvenience to our customers."

Judging from comments left on McAfee support forums, the snafu is causing considerable problems for many customers.

"How much longer before McAfee finds a fix or has the update 5959 to resolve this problem?" one admin wrote. "We are a school district and have over 5000 computers being effected by this DAT file. This Extra.dat files looks like it will work but guess what the 5958 update has already been applied so this will not work for us."

The infrastructure security head, who was working in one of his firm's UK offices, said about 30 percent of the company's PCs were affected, in part because admins disconnected working machines from the network after learning about the glitch. So far, his team has been able to bring only about 5 percent of the disabled machines back online.

The snafu causes VirusScan Enterprise to falsely flag svchost.exe as infected with malware known as Wecorl.a. More from the Sans Institute here. ®

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