On July 11th, 2012 Symantec Security Response started receiving reports of customers experiencing blue screens after applying the July 11th revision 18 definitions. Machines may continue to blue screen after they reboot.This problem only appears to occur on Windows XP machines. The root cause of the problem is unknown at this time.
Security Response is treating this issue with the utmost priority and is actively seeking a solution. Further information will be provided as soon as it becomes available.
Orla
Symantec Security Response