Buggy McAfee update slams Windows XP PCs

[Broni]

http://isc.sans.org/diary.html?storyid=8656

McAfee's "DAT" file version 5958 is causing widespread problems with Windows XP SP3. The affected systems will enter a reboot loop and loose all network access. We have individual reports of other versions of Windows being affected as well. However, only particular configurations of these versions appear affected. The bad DAT file may infect individual workstations as well as workstations connected to a domain. The use of "ePolicyOrchestrator", which is used to update virus definitions across a network, appears to have lead to a faster spread of the bad DAT file. The ePolicyOrchestrator is used to update "DAT" files throughout enterprises. It can not be used to undo this bad signature because affected system will lose network connectivity.

The problem is a false positive which identifies a regular Windows binary, "svchost.exe", as "W32/Wecorl.a", a virus. If you are affected, you will see a message like:

The file C:WINDOWSsystem32svchost.exe contains the W32/Wecorl.a Virus.
Undetermined clean error, OAS denied access and continued.
Detected using Scan engine version 5400.1158 DAT version 5958.0000.

McAfee released an updated DAT file, and an "EXTRA.DAT" file to fix the problem. An EXTRA.DAT file is a patch to just fix the bad signature. McAfee's support web sites currently respond slowly and are down at times, likely due to the increased load caused by this issue.

Several readers reported that this procedure worked to recover:

1 - Boot the system in "Safe Mode"
2 - copy extra.dat in c:/program files/common files/mcafee/engine
3 - reboot.

If you lost "svchost.exe", then you need to copy it back to c:/Windows/system32/svchost.exe while in safe mode. This fix has to be applied locally at the workstation. However, it may be possible to do this remotely if your workstations support Intel's "vPro" technology. We should have a link to instructions shortly.

Additional information from McAfee: http://community.mcafee.com/thread/24056?tstart=0
McAfee Knowledgebase Article: https://kc.mcafee.com/corporate/index?page=content&id=KB68780
EXTRA.DAT file: http://home.mcafee.com/VirusInfo/VirusProfile.aspx?key=265240.

[rthompson80819]

Basically same story, different source, and a few different details.

http://www.comcast.net/articles/news-technology/20100421/US.TEC.McAfee.Antivirus.Flaw/

[Broni]

Fix posted at BleepingComputer: http://www.bleepingcomputer.com/forums/topic311599.html

[BC_Programmer]

An interesting demonstration of "the cure is sometimes worse then the disease" if I ever saw one.

[Broni]

I assume, you're referring to McAfee as a disease   

[rthompson80819]

That's one of the reasons I have automatic updates turned off in Windows and av programs.  I always do the updates, but wait a few days to make sure there are no bugs.

[Broni]

Well, with AV program it may work to your disadvantage.
I think, it's better to keep your AV up to date and keep a fresh image of your drive.

[James1431997]

Haha. We use McAffe at school. Only some computers worked (the ones turned off before the update) and we rely on our IT for everything (registers being a prime example.) Taking ages to fix, though, bearing in mind we have 1500 PCs running McAfee.