Security researchers at Sana Security are warning of a new type of malicious software designed to steal usernames and passwords from web surfers. The malware, dubbed "rootkit.hearse," uses rootkit cloaking techniques, making it extremely difficult to detect.

In order to steal information, however, the software must first be downloaded onto a user's system. This can be done by tricking the user into downloading the malicious code, or by infecting a computer with some other form of malware. Once installed, it sends the sensitive information to a server in Russia, that appears to have been in operation since 16 March, Sana said.

The software has two components: a Trojan horse application that communicates with the Russian server, as well as rootkit software that cloaks the malicious software from system tools and anti-virus programs. Sana has observed the software being downloaded in conjunction with the Win32.Alcra worm.

Rootkit.hearse uses the same kind of cloaking techniques made infamous by Sony's XCP rootkit software, making it hard to find, according to Sana chief technology officer Vlad Gorelik.

As of late Monday, rootkit.hearse was detected by only five of the 24 security products that Sana tested it against, though that number is expected to change as word gets out. "I'm sure that there are others who are beginning to pick it up at this point," Gorelik said.

The Trojan horse software spends most of its time lurking in the background, but it springs to life to communicate with the Russian server whenever a user hits a website that requires authentication. The software can read password information as it is typed or even when it is automatically stored and submitted by features like Internet Explorer's AutoComplete.

As of Tuesday, the Russian server had stored about 35,000 unique user names and logins that could be used on about 7,000 different websites, including banking, auction and social networking sites, Gorelik said.

Sana informed the Russian ISP for the site in question on Monday, Gorelik said. Sana declined to name the ISP in question. As of Tuesday morning, the Russian site was still operational, he said.