It sounds like something out of a bad UHF sci-fi flick, but it's actually a growing problem on the Internet. These days, fraudsters are moving past the point of spyware and adware and are instead planting remotely controlled click fraud bots onto unsuspecting Internet users' computers. The bots are hard to detect and can be programming to rack up PPC clicks on sites designated by the bot's creators.

From Help Net Security:

According to the data collected so far, the scam is exploiting a global network comprising more than 34,000 zombie computers (those infected by the bot).

The bots are controlled remotely through several Web servers. This allows the perpetrators to define, for example, the web pages on which the adverts are hosted or the maximum number of clicks from any one IP address in order not to arouse suspicions. Similarly, the number of clicks from the bot can be monitored as well as the computers online at any one time. The system used can evade fraud detection systems by sending click requests from different, unrelated IP addresses.

That could spell more bad news for search engines as they try to fight fraud and more bad news for advertisers that must continue sorting out content syndication sites that are part of these types of networks.