Malware that secretly clicks on ads in order to defraud advertisers might seem generally harmless to infected machines, but can serve as a gateway to more serious infections, according to a report released today by Damballa.Clickfraud malware has been showing up a lot this year, said Stephen Newman, CTO at security vendor Damballa, with about 32 million active infections spotted in the company's customer base during the first half of this year, or about 210,000 per day.According to the Association of National Advertisers, it costs US businesses about $6.3 billion a year in wasted ad money.But how much of a threat is it to enterprises with infected machines?If it sneaks in past initial security controls, the malware tries to be as undetectable as possible while it racks up the fraudulent ad clicks in the background."It doesn't pose any immediate risk to the business," said Newman. That's a challenge for enterprise security professionals who have to prioritize which threats they address first and put off dealing with clickfraud-related infections.That's because click fraud is often just the first invader of a potentially long chain.Once the machine is part of the botnet, the criminals aren't going to let go of it easily.Once the first clickfraud campaign is over, the botnet operators will sell the machine to another criminal group. And when that campaign is done, it gets resold again.At some point in the chain, it will get used for ransomware or another dangerous attack."This is a significant problem for security teams inside enterprises," Newman said. "It is critically important for security teams to not only discover which systems are compromised, but to track changes in behavior over time."Those changes can happen quickly -- in one threat that Damballa analyzed, the criminals installed three additional click-fraud infections and CryptoWall in just two hours.This particular threat, which Damballa named RuthlessTreeMafia, starts out with a phishing email that installs the Asprox botnet malware. That, in turn, gets an update from its command and control center that includes a malware downloader, a rootkit and a click-fraud installer.This is followed by CryptoWall, which takes just seconds to encrypt all the files on the machine. However, according to Damballa researchers, the click-fraud activity continued in the background, even after all the user files were encrypted.And it gets worse -- after the malware finally kills its host, it can move on to other parts of the network, and start the cycle over with new machines.