Signaling criminals' growing interest in attacking non-Windows computers, researchers have discovered banking fraud malware that targets people using the open-source Linux operating system.

Hand of Thief, which was recently discovered by researchers from security firm RSA, sells for about $2,000 in underground Internet forums and boasts its own support and sales agents. Its functionality—consisting of form grabbers and backdoor capabilities—is rudimentary compared to Windows banking trojans spawned from the Citadel or Blackhole exploit kits, but that's likely to change. RSA researcher Limor Kessem said she expects Hand of Thief to become a full-blown banking trojan that includes more advanced features such as the ability to inject attacker-controlled content into trusted bank webpages.

"Although Hand of Thief comes to the underground at a time when commercial trojans are high in demand, writing malware for the Linux OS is uncommon, and for good reason," Kessem wrote. "In comparison to Windows, Linux's user base is smaller, considerably reducing the number of potential victims and thereby the potential fraud gains."

She also said that the open-source model Linux is developed on makes the OS less susceptible to attacks that remotely execute malicious code by exploiting security bugs. That viewpoint is popular among many open-source advocates, but it's also the source of heated debates among security researchers. The number of Linux machines running Apache and other Web servers that are infected by Darkleech and similar exploits—recently estimated to be in the 20,000 range—suggests the platform isn't out of the reach of motivated attackers. What's more, contrary to popular beliefs, serious Linux vulnerabilities can sometimes linger for years. In fairness to Kessem, she said a Hand of Thief sales agent recently suggested using social-engineering attacks to infect users of the open-source OS.

Leaving that debate aside, Hand of Thief developers said the trojan has been tested on 15 different Linux desktop distributions, including Ubuntu, Fedora, and Debian. They also said it supports eight environments, including Gnome and Kde. The malware functions include a form grabber for both HTTP and HTTPS sessions running on Firefox, Google Chrome, and a host of Linux-only browsers. The trojan also blocks infected machines from accessing addresses that offer security updates and antivirus software. It contains defenses to prevent it from running on virtual machines to make it harder to be reverse engineered by white hat hackers and competitors.

"The developer wrote a basic administration panel for the trojan, allowing the botmaster to control the infected machines reporting to it," Kessem wrote. "Captured data includes information such as timestamp, user agent, website visited and POST data. Hand of Thief also exhibits cookie-stealing functionality."

The $2,000 price tag strikes Kessem as overpriced compared with Windows trojans. That may be true. But given the large number of security-conscious computer users who regard Linux as a relatively hacker resistant haven, Hand of Thief marketers may position it as a premium service for attacking high-value targets who can't be penetrated otherwise. Further, given the vast improvements Microsoft has made in the past six years securing recent versions of Windows, malware writers may be interested in expanding the range of machines they can attack. Researchers recently unearthed a new banking trojan targeting Android users.

On the other hand, there are few if any reports of comparable malware targeting Mac users. It's hard to know precisely what to make of Hand of Thief, but it's worth keeping an eye on.

Updated second paragraph to correct attribution of "Hand of Thief" title.