McAfee pushed out a virus definition update, 5958, at 14:00 PDT that causes false positive identification of the critical Windows system file svchost.exe. Machines running Windows XP Service Pack 3 using the 5958 definitions will delete the file, causing many key Windows services to fail to start. The Windows file is being mistakenly detected as W32/wecorl.a. Failure to start svchost.exe causes Windows to automatically reboot, hindering repair efforts. McAfee’s support forums have at least partially been crushed under load. Repair likely involves SAFE MODE manipulations possibly beyond the normal expertise of many users. http://www.nnsquad.org/archives/nnsquad/msg03404.html
Toms Blog on Life and Livingness