MsMpEng.exe problems with MSE, not OneCare

I am using Windows XP and facing 100% CPU usage since I installed Microsoft Security Essentials. I know that Windows Defender comes by default with Vista or Windows 7 but I’m not sure whether it is the part of Windows XP. Is it part of MSE or OneCare? Because whenever I ran MSE or OneCare I noticed that CPU usage goes upto 100% and it freezes my computer completely. Also when I start Task Manager I see MsMpEng.exe program running and it consumes the highest CPU resource. Can you guys suggest me something regarding this?

I have never used OneCare or Microsoft Security Essentials but as far as MsMpEng.exe is concerned, it is found with both MSE as well as Windows Defender. But CPU usages use to go high only when I schedule it to scan the system. Are you also doing the same? Anyway, I don’t think you can configure a task priority for the scan. It will run on the normal priority itself.

Before I can answer you would like to know few things. That is before you installed MSE, did you removed OneCare using the OneCare Cleanup utility? Also was your OneCare subscription valid/expired before you removed it? Other than this have you also installed any other antivirus program such as Norton or McAfee application?