I had to remove it about 3 times in a 2 week period, and reported it to Microsoft at their www.microsoft.com/reportascam
.
Do this is if turning your computer OFF immediately doesn't work because they've looped the dialog box:


1. Hit ctrl-alt-delete
2. select task manager
3. choose web browser program and
4. end task

Found info onsite as to how to get it off- temporary fix, but better than un-installing Norton or McAffee, which is one recommendation of theirs

Haven't had a re-occurence in about a week now..

I"m assuming a permanent fix would be to go the uninstall route