It is unclear to me who are the swindlers and how they benefit. Are people clicking on competitor's links to drive up costs?
Not everyone who clicks will purchase, but that's what advertising is about. Suppliers are working on more directed techniques, as an example Microsoft is running ads for their search tools, claiming they have a technique to weed out, a child looking at furniture for her doll house.
Now the destructive clickers are advertisers trying to 'get even with' competitor advertisers by 'clicking them out of business'; clicking sufficiently to run the other guy's advertising budget sky-high and/or using up all the other guy's self-imposed allotment of click-throughs so his ad won't appear any longer for that day/week/month, etc. It is sort of like what is done with spammers with a toll-free number. You see an 800 number in some spam/scam and you call it just to basically annoy and hopefully bankrupt the owner, although of course we do not describe it that way; we try to give our efforts a 'good-faith motive' on all those phone calls. _But if we can 'teach the spammer' how expensive it is to spam and give good, bonafide contact information in the process of his spam_, we feel we have done a good job.
Or maybe they are not 'competitive advertisers' at all, but simply netters who cannot see the difference between one form of spam/scam (the informal do it yourself kind) and the more 'officially approved' kind which comes through Google Ad Sense, so they take the attitude 'down with all of it'. PAT]