Mytob's Hackers May Spawn Unstoppable 'Super Worm'

There's mounting evidence that a group of industrious hackers is working on an especially destructive "super worm" that could spread from PC to PC indefinitely, or until it ran out of targets to infect.

The most recent clues are found in the slew of Mytob worms released this week that signal a systematic development process that may indicate," a security researcher said Friday.

Six variations of the Mytob worm have been spotted since Wednesday, June 1, by anti-virus vendors such as Symantec, bringing the total count since its debut four months before to more than 100. But prolific as it is, Mytob's reproductive habits aren't what draws attention from some experts.

"The variants are numbered, just as if it was a regular commercial program," said Carole Theriault, a security consultant at U.K-based Sophos. "One will be number version 1.0, the next 2.0. They're trying out things, different things in each," she said.

"They're following a carefully planned strategy to allow the worm to develop. By issuing multiple threats, all of which are tweaked slightly differently, they may be searching for the best code that will help them create a super worm."

A so-called super worm has been the bugbear of anti-virus researchers, and supposedly the Grail for hackers. The term is usually used to describe a worm that could spread indefinitely, or until it ran out of targets to infect.

The makers of Mytob, which includes code borrowed from earlier malware MyDoom and Rbot, appear to be a group calling itself "Hellbot," said Theriault. The group effort makes it possible, she went on, to crank out variant after variant, essentially flooding the Internet with copies and trying out techniques ad nauseam.

All Mytobs share characteristics such as hijacking addresses from compromised PCs to spread using its own SMTP engine, dropping in a backdoor Trojan so more malicious code can be added to the infected system, and try to shut down security software already on the computer. The Hellbot group's been busy, Theriault added. As of Thursday, almost 50 percent of all malicious code Sophos was blocking consisted of Mytob variants. U.K.-based filtering firm MessageLabs reported similar percentages. According to Maksym Schipka, an anti-virus researcher with MessageLabs, Mytob represented at least 35 percent of all malware this week. In one 24-hour span, said Schipka, MessageLabs intercepted over 1.1 million copies of the worm. Also active this week was the Bagle family of worms and Trojan downloaders, but researchers said that the spike in both groups, Mytob and Bagle, was probably just a coincidence. "It's unusual, and interesting, that they're happening at the same time," said Theriault, "but there doesn't seem to be any connection at the moment." The glut of Mytobs, however, did set one record. Several security firms pegged Mytob as the most pervasive piece of malware for the month of May, the first time that malicious code created in 2005 pushed older worms and viruses off the top spot. Both Sophos and Kaspersky Labs, a Moscow-based anti-virus software maker, had a Mytob variant in the number one spot on May's chart.