I have 3 XP Pro Service Pack 3 systems at my house with all the most recent updates from Windows Update.
Today one went down around 5 PM eastern time. System hung and when rebooted upon user login would hang again.
Booted the system to safe mode and manually ran Microsoft Security Essentials and 2 other anti-malware/virus software. All clean.
About 2 hours later while researching the issue with from 2nd XP machine, 2nd machine hangs and has same symptoms.
I boot it to safe mode and when I go to run Microsoft Security Essentials manually, I notice virus definition updated just before system crash/hang.
I check 1st machine and see it's issue started after it updated to virus definition 220.127.116.11.
Went to 3rd XP machine, and found Microsoft Security Essentials had virus definition 1.169.2690.0 and system boots and runs fine. To test my theory, I forced an update from Microsoft Security Essentials. Once updated to 18.104.22.168 was finished system hung. Booted system normally and it too hangs during login same as first 2 machines.
Went back to 1st machine, in Safe mode and attempted to remove MSE. But you can't while in Safe Mode.
So I went to C:\Program Files\Microsoft Security Client folder and renamed all the .exe files for MSE by adding a 2 at the end:
Files I renamed:
Rebooted system normally and since MSE is unable to load, system came up and ran normally. I was then able to remove MSE and installed a 3 License copy of McAfee Internet Security I had purchased for a customer. Issue resolved. Repeated this on other 2
XP machines and all are up and running fine now after 4 hours of work. Multiple reboots and relogins and issue has not returned since removing MSE.
About to see if the issue happens with a Vista machine which I know has not been updated in over 2 weeks and will try to attempt to repeat symptoms on a Windows 7 machine also.