Many enterprises, including police departments and hospitals in the US, were hit by a false positive from McAfee on Wednesday that labelled a core Windows file as potentially malign.
A detection update from McAfee (DAT 5958) falsely labelled the svchost.exe as the Wecorl-A virus, sending a core Windows system file into quarantine in the process. Infected computers became inoperable and went into a continuous reboot cycle. Clean up operations were further complicated by the fact that the dodgy update disabled network access.
McAfee responded to the problem by withdrawing the definition update and later releasing a clean one. The security giant also published advice on how to manually fix affected computers. The influx of interested parties trying to look up this advice through McAfee's forum caused the site to become unavailable for a short time on Wednesday evening.
Cybercrooks wasted little time in exploiting the situation for their own purposes, poisoning search results so that links to scareware portals appeared prominently in indexes. As a result users are advised to be especially careful if they choose to search for information on solving the problem. Getting advice directly from McAfee is a far better option.
The timing of the update - mid-afternoon on Wednesday (European time) - meant that US enterprise systems configured to automatically apply new updates were among those worst affected. Reported victims include Kansas City Police Department and and the University of Kansas Hospital and about a third of the hospitals in Rhode Island. PCs also went haywire at Intel, the New York Times reports, citing Twitter updates from workers at the chip giant as a source.
First hand experiences from an Iowa community emergency response centre, ironically running a disaster recovery exercise at the time, can be found in a posting to the Internet Storm Centre here. The Register has heard from a senior security officer at a net infrastructure firm that was also hard hit by the snafu, as reported in our earlier story here.
Some commentators compared the effect of the update to the infamous Blaster worm. It's unclear, however, if any item of malware has so effectively floored so many systems in such a short space of time.
McAfee is seeking to downplay the effects of the incident, saying that few consumers were affected while apologising to those hit:
McAfee is aware that a number of customers have incurred a false positive error due to this release. Corporations who kept a feature called “Scan Processes on Enable” in McAfee VirusScan Enterprise disabled, as it is by default, were not affected.
Our initial investigation indicates that the error can result in moderate to significant issues on systems running Windows XP Service Pack 3.
The faulty update was quickly removed from all McAfee download servers, preventing any further impact on customers. We are not aware of significant impact on consumers.
False positives affect all anti-virus software vendors from time to time. Problems are particularly severe, as in this latest case, when a core Windows file was targetted.
As previously reported, the industry's approach towards minimising the number and severity of false positives has been to make greater use of whitelisting.
Quite why that technique either wasn't applied in the McAfee case or failed to work properly is a key question for McAfee's quality control engineers to consider in the wake of Wednesday's massive snafu. ®