Perhaps you, like me saw a rash of sites giving the error "Internet explorer cannot open the Internet Site" yesterday.  At first I thought one of my machines was messed up.  Then I saw it on another machine.  This one running XP.  A virus perhaps?  I can't recall doing the same thing on both machines.  How would I get a virus on both?  A worm maybe?  Updated the antivirus just in case.  This morning the errors seemed to be gone but still the mystery.  What caused it?

It appears that a tool called SiteMeter was causing the problem.  Mystery solved.  More detailed information here.