It means that at least one person that processed the registrations was using a windows system that is now infected. That stupid blaster virus then sent email with a forged From line as if it was sent from you, then the spammers picked up that never released email address and added it to their spam list.
Makes me wonder if the virus was build by someone wanting to find a lot of valid email addresses that were not otherwise available.
A simpler explanation is that the proceedings on the IETF website include a list of attendees, with email addresses...
Colin