I was away for a few weeks and I suspect that my PC has been tampered
with. I'm using XP Home and the login is secured by a password but I
know you can bypass it:
http://www.experts-exchange.com/Operating_Systems/WinXP/Q_20348448.html

I need to verify ALL files (several hundred thousand) not just one or
two. What's an easy method to verify the last time each file was last
accessed? Thank you.

Hi webmal,

Go to Start, Search, for Files and Folders, click on ALL Files and
Folders, Look in:  Select your hardrive.

Below the Look in box you'll see When was it Modified?  Scroll to:
Specify dates, Modified Date.

In the From box type in the first date you were away, and the To box
type in the last date when you returned.  (Or select other dates that
apply to your concerns.)

Click on Search.  You'll see a list of all files that were modified
while you were away.


Search:

Personal knowledge


Best regards,
tlspiegel

Hi webmal,

Thank you for the nice rating!  :)

Best regards,
tlspiegel

If tampering did occur they may have tried to install spyware, the
gift that keeps on giving.  There is a veritable spyware epidemic, and
the FTC is only just now wading in to the matter.

http://answers.google.com/answers/threadview?id=330873

Here are two links explaining the spyware threat from today's Google News 

FTC
http://informationweek.securitypipeline.com/news/18901899

BBC
http://news.bbc.co.uk/2/hi/technology/3633167.stm

You might want to check this out
http://support.microsoft.com/default.aspx?scid=kb;en-us;310399&Product=winxp