it's possible you might have got hit with spyware.ispynow. this happened to many people last night including myself, around 18:30EST. it took me a while to figure it out... you'd know if you got something like this
http://www.spywareremovalblog.com/remove...
for some reason, the anti-virus programs out there are having a hard time finding it, but you can possibly find it on your PC by looking here:
C:\Documents and Settings\Owner\Application Data\Google
the file should be 5 letter, 7 digit code, accompanied by the "windows firewall" icon. mine was: ggqjh225xxxx.exe (i forget the other digits). the popular ones seem to be: runhh6110411.exe, and: xtgoj6119471.exe
to delete the file you will have to reboot in "safe mode", then go to the address above and delete the file. no anti-virus software required.
hope this helps. i know a lot of people have been burned by this today.