If you're an advertiser with the search engines, it's bad enough that people click on your ads with no intention of buying anything. Worse, they may do this for money or to drain your advertising budget. This is click fraud. And it's not just humans doing it anymore.
"All Warfare is based on Deception."
-- Sun Tzu's Art of War
Click Fraud
"Mesotheliomia" is not a location in Transylvania. It is a rare form of cancer caused by asbestos. What does that have to do with SEO? Well, certain professionals like lawyers are very interested in optimizing their sites for such a key word to get the eyeballs of potential customers. Since organic optimization is an intensive process, however, most litigation lawyers (drooling at the thought of a cut of a massive settlement) will simply bid as high as ten to fifteen dollars per click on pay-per-click networks.
Such a highly competitive key word can attract unscrupulous webmasters to begin clicking on their own ads (or unscrupulous litigators clicking on their competition's ads so as to drive their ad accounts dry). Here we have a basic form of click fraud, fraught with chances of discovery by advertisers or Google itself, with a limited amount of money that can possibly be earned. After all, how many times can you possibly click on your own ads, and how many people can you hire to click on them for you? It makes sense for perpetrators of click fraud to think that "it has to be easier than this."
Automation
Enter zombie computers and bot networks. After years (an eternity in Internet times) of using zombie computers to send spam emails to email addresses, spammers and botmasters have zombie computers which they control remotely without any awareness from the users. Now they've started turning their bots and zombie computers from schemes like denial of service, trust fraud, and spamming to another fraudulent venture, click fraud.
Search Engine News 
