Shoutbox

Someone online today IMd me and said "Hey is this really you? http://messengertools.org/contactinfo.exe" or something like that, I downloaded it and opened it opened up a chat window with every person online and said that that person had just said to me.  I can't go on msn now because it'll just do it again, also when I'm on the internet, it will open up the find option (control+F) and paste "www.messengertools.org/msn.php?session=gGvc1040&user=$msnaddy" into it.  I've ran anti-virus,spyware,ad-aware scans and nothing came up.  Someone please help me!