From McAfee AvertLabs:
“McAfee is aware that a number of corporate customers have incurred a false positive error due to incorrect malware alerts. Our initial investigation indicates that the error can result in moderate to significant performance issues on systems running Windows XP Service Pack 3.
The 5958 DAT has been removed from McAfee download servers, preventing any further impact to corporate customers. McAfee teams are working with the highest priority to support impacted customers and plan to provide an update virus definition file shortly. You can view information at https://kc.mcafee.com/corporate/index?elq_mid=2362&elq_cid=757526&page=content&id=KB68780 (NOTE: system is currently slow) or the McAfee Community at http://community.mcafee.com/docs/DOC-1374/”