[TELECOM Digest Editor's Note: As for myself, I cannot really picture
> 'five hundred thousand zombie computers scattered across three
> continents'. If so, under whose coordination? A gang of crackers all
> working in concert to cheat some advertiser's competitor, by running
> up his advertising bill? Seems sort of improbable to me. PAT]
It's not so hard to imagine if you consider the way viruses are spread to launch spam, DDoS attacks, etc. The virus authors or cracker-gangs aren't necessarily working to cheat competitors; they're just being disruptive.
--gregbo