After lying low for several weeks, hackers responsible for spreading the Storm Trojan have returned to the attack with e-mail that leads to an exploit-filled Web site and a laughing cat, researchers said.
Storm, a.k.a. Nuwar, a.k.a. Peacomm, is a Trojan horse designed to compromise Windows-powered computers, then add those machines to a growing botnet. Although the size of the botnet acquired by Storm has been disputed, the most conservative estimates put it in the hundreds of thousands.
The malware has been seeded using several attack vectors, but the most common have been e-mail campaigns that contain attachments, or which link to malicious Web sites. Those sites then infect visiting vulnerable PCs using drive-by downloads or by convincing users to click on additional links that then download an executable.
Attacks typically come in waves, researchers have noted, that rise, crest and then subside, while the hackers behind the botnet have become infamous for crafting persuasive messages and tricking users into infecting themselves.
"After a few weeks of low activity from the Storm gang, they... changed the e-mail messages and also the website," said Patrik Runald, a researcher with Helsinki-based F-Secure, on the company's blog.
Starting yesterday, Storm's backers began sending messages bearing text that read, "Here is the new Psycho cat card," and contained a link to a URL. Recipients who click on the link reach a site posing as a humorous greeting, with a Shockwave clip of a laughing kitten, complete with soundtrack, said McAfee's Dmitry Gryaznov.
The page, however, is loaded with multiple drive-by exploits as well as links to the "SuperLaugh.exe" executable. That file is actually a recent variant of Storm.
"Of course, pretty much wherever you click on the page, you get nothing but Nuwar," said Gryaznov on his company's research blog.