Why do you care? If you are running Windows XP you are vulnerable to a staggering amount of exploits including rootkits, and buffer overflow attacks. Many malicious programs will use these exploits to get into your systems without your (or your anti-virus’s) knowledge. One of the best ways to prevent Malware is to use a sandboxing program to isolate your system. Sandboxie is one such program. Check out these excellent posts about Sandboxie:
Sandboxie, an excellent sand boxing utility, is now available in 64-bit flavor. A sand box is a program that separates another running program from the rest of your system. I recommend Sandboxie to many of my clients (especially those running XP) as and added level of protection against Malware. For more details about Sandboxie check out this video review (in 3 parts).