The recent volatility in the value of Bitcoins hasn't prevented cybercriminals from cooking up new ways to distribute malware engineered to mine the currency using compromised computers.

Security researchers at ThreatTrack Security have uncovered examples where the infamous Blackhole exploit kit is being used to distribute a variant of the Fareit information-stealing Trojan onto Windows PCs.

Of course, Fareit has other capabilities besides slurping sensitive information from compromised PCs and sending it back to a remote server. It can also use your computer as a node in a DDoS attack. But some variants also download an additional file onto a compromised PC, save it to a temporary directory, and then execute it, using your PC for its compute power (and hiking up those energy bills). This is the part that interests the Bitcoin baddies. The malware-flingers are using Fareit to surreptitiously install a Bitcoin mining utility.

"Fareit is also known to steal passwords," explained Chris Boyd, a senior threat researcher at ThreatTrack. "In a lot of cases it drops Rogues (like Winwebsec), search redirectors (like Medfos), and infostealers (like Zbot and Cridex)."

"It's interesting that in this case, they (the people who configured this variant) decided to drop a [Bitcoin] miner."

The Blackhole exploit kit is the weapon of choice for running drive-by-download attacks from vulnerable websites. Its application in an attack ultimately designed to distribute rogue Bitcoin mining software is a sign that mining the virtual currency is entering the mainstream of the underground economy, joining rogue antivirus and ad-redirection scams as a way to earn a dishonest living.

ThreatTrack researcher Jovi Umawing said her team had initially found the Blackhole exploit throwing out the Fareit Bitcoin mining attack hosted on a dubious Russian adult website. She said the researchers had been following links from a redirector URL they had been monitoring.

"While malware distributing Bitcoin miners isn't new, we believe this distribution is fairly new," Boyd explained. "There have been a couple of recent incidents of malware dropping a rogue miner on systems (a couple weeks ago there was a variant of the Dorkbot worm dropping a miner), highlighting the growing popularity of Bitcoins to criminal groups."

More details on the attack can be found in ThreatTrack's blog post, containing screenshots of the attack and more details on the malware, here.

Bitcoin is an online decentralised virtual currency based on an open-source P2P protocol. Cybercrooks have latched onto the popularity of the currency by running digital wallet stealing attacks as well as earlier offensives that mine bitcoins using compromised computers, previously seen using variants of the infamous ZeuS banking Trojan. Cybercrooks have also set up fake sites that pose as Bitcoin currency exchanges in order to run phishing attacks.

A comprehensive run-down of all these forms of malfeasance can be found in a blog post by security tools firm AlienVault here. ®