My daughter caught this one, aswell. Vista on PC world pc. It evaded a fully up to date AVG and both the BT modem router firewall and MS's firewall on the pc.
It was a "Trojan downloader" and it had downloded 3 other "severe" nasties.
It probably came in via one of those music file sharing apps that teenagers love. ("Life wire riddem" comes to mind.)
I ran avg, and installed McAfee, and whilst those two found "bits" of whatever the thing had invited on to the pc, they did not kill it all.................so, machine went to nice local techie man for complete wipe, copy and serious security grilling of music, piccies and doc.s, and the re-install of Vista, followed by re-copy of docs etc.. Seems OK now, but I do run manual McAfee scans aswell as the scheduled ones just in case.....................bolting door after...........??
Oh, yeah - I'd set her up as a non-admin, but she often went on as admin to download new dodgy file sharing stuff..................