A notorious online gang known for its prolific phishing operations has expanded its means of attack, potentially putting more PC users at risk of losing personal data.

The Rock Phish gang surfaced around 2004, becoming well-known for its expertise in setting up phishing sites, which seek to trick people into divulging sensitive data, as well as for selling phishing kits designed for less technical cybercriminals.

Now, the phishing sites linked with the Rock Phish gang are being rigged with a drive-by download, a type of attack that can infect a PC with malicious software without any interaction by the user, researchers from vendor RSA said Monday.

The one-two punch means that even people who go to the phishing site but aren't fooled into inputting their personal details could still be infected, wrote Uriel Maimon, a senior researcher, on RSA's blog.

The phishing Web site tries to exploit any software vulnerabilities, and if it finds one, will then load the Zeus Trojan onto the PC. Zeus is particularly dangerous: it can collect data on forms, take screen shots, pilfer passwords from browsers and remotely control the computer, Maimon wrote.

Zeus also comes in at least 150 flavors. One of the phishing kits being sold now for US$700 masks how Zeus appears to security programs. That kit uses a binary generator, which creates a new binary file for Zeus for every kit.

Antivirus programs uses signatures, or data files, that describe what malicious programs "look" like in order to be detected. But creating new binaries can render security programs blind. Most of the popular antivirus programs can't detect the variants.

"These files are radically different from each other, making them notoriously difficult for antivirus or security software to detect," Maimon wrote.