According to SANS Internet Storm Center, a recent McAfee anti-virus software update is returning false positives that are causing problems on systems running Windows XP SP3. The problem appears to be that McAfee is flagging the system file svchost.exe as malicious, misidentifying it as a virus named W32.Wecorl.a. The problem affects the antivirus update (DAT 5958) released on April 21. The resulting problem is that machines are forced into an endless boot loop. McAfee is recommending that users download an updated anti-virus signature (DAT 5959) on an unaffected computer, copy it to a USB drive, start the affected machine in safe mode with network support and install the new signature. The problem does not appear to be fixable from a central management console; each computer is estimated to take about 30 minutes to fix.
Read the full report posted on SANS Internet Storm Center: McAfee DAT 5958 Update Issues