A Russian porn site is delivering malware that uses the victims' computers to mine bitcoins, according to research from ThreatTrack Security.

The malware, named "Fareit," has been circulating on the Internet for at least six months and infects Windows computers. It has been modified to "mine" the virtual currency, said Dodi Glenn, director of AV Labs at ThreatTrack Security, which was spun off from GFI Software last month.

Bitcoin is a virtual currency that can be transferred for free using peer-to-peer software. New bitcoins are created by mining, or contributing computing power that is used to verify transactions, which are entered into a public ledger called the blockchain.

New blocks are created about every ten minutes, and miners who create a new block are rewarded with 25 bitcoins, the preset reward set by the Bitcoin's system's pseudonymous creator, Satoshi Nakamoto.

Fareit is general family of malware that in this case has been modified to install a bitcoin mining application called "CG Miner." A look inside the software package installed shows a script comment written in Cyrillic, according to ThreatTrack's writeup.

The hackers then use the victim's computer to compute parts of the blockchain and then send that data to Russian domains, Glenn said. "You're then part of their particular ring," he said.

Bitcoins targeted

This particular variant of Fareit was submitted to VirusTotal around January, but there is other malicious software engineered to mine bitcoins created as recently as three weeks ago, Glenn said.

Mining bitcoins on compromised computers is a less intrusive way of acquiring the virtual currency than stealing the coins from people's computers, Glenn said. Victims may not even notice the malware running on their computer, while those who lost bitcoins certainly would.

Fareit was planted on a Russian porn site, Glenn said. It is delivered to a vulnerable computer by the Blackhole exploit kit, which attacks a person's computer and looks for vulnerabilities upon visiting a website. Fareit is also capable of stealing information from a computer as well as conducting distributed denial-of-service attacks (DDOS), Glenn said.