A couple more reports on that too:
http://blogs.zdnet.com/Spyware/index.php?p=735
http://www.eweek.com/article2/0,1895,1906915,00.asp

If you cast your mind back to last year, there was a case where a major commercial ad network was serving up another exploit: http://www.theregister.co.uk/2004/11...server_attack/ - the fallout from that was pretty nasty.