A new report shows bad actors online are using ad networks to infect personal computers will malware, reports ClickZ.

The report comes from Finjan Malicious Code Research Center and shows cyber-criminals are becoming more creative with how they reach out and take control of computers. In some instances they infect a specific ad with a virus that hits every computer the ad loads on. In others, ad networks are formed where the basis of payment is how many PCs are infected with malicious code.

Viruses can be downloaded and installed and begin logging keystrokes, used as spam servers or anything else, without the user's knowledge. The software is relatively cheap and instances are hard to track, since infected sites may change when the same computer goes back to them to avoid detection.