Alternatively, check the message for the originating IP address. Chances are, they're all from the same computer. Details of how to do this here:
http://www.cableforum.co.uk/board/sh...ad.php?t=10441
Then find out where to report abuse using this:
http://www.dnsstuff.com/
(although it's not working for me at the moment)
If it turns out to be an NTL customer you can use the online form here:
http://www.ntlworld.com/netreport/
Then simply report that you are getting viruses and the ISP
should quarantine them until they've cleared up their computer.