I won't know until I go over there in a few hours, but my friends business' main computer has been having this problem as he describes it with "constant lock-ups and slow down." I remember long ago when I went over I kept seeing a lot of programs with just a combination of letters andbslr.exe etc in Task manager. Typically I go into safe mode and manually delete all the random folders he's managed to get, and constantly close them in Task manager as they re-open.
I'm not overly familiar with Windows XP security - Is there any program better for XP than another I can get to help him avoid these issues? Bit Defender possibly?