Basically, an auto-update feature of a virus checker does that. Just as "we" create viruses, "we" create the anti-bodies too.

Subscribing to the update is a purposful thing; it doesn't have to act like a virus. Hmm, except to get it into the hands of people who really need it!

So, we need a mass-inoculation where a copy of a good, free, virus checker is mailed to everyone. That can be smapped once, though, and doesn't need to self-propagate beyond that.