Cyber Attack Code Starts Killing Infected PCs

The botnet-driven cyber attack on government, financial, and media sites in the U.S and South Korea includes a newly discovered danger: The malicious code responsible for driving the distributed denial of service attack, known as W32.Dozer, is designed to delete data on infected computers and to prevent the computers from being rebooted.

"Your machine is completely hosed at this stage," said Vincent Weafer, VP at Symantec Security Response.

The malicious code includes instructions to start deleting files when the infected computer's internal clock reaches July 10, 2009. That's today.

According to Weafer, the malicious code will attempt to locate files with any of more than 30 different extensions, such as .doc, .pdf, and .xls, copy the data to an encrypted file that's inaccessible to the user, and then overwrite the data in the original files. It targets files associated with office, business, and development applications.

The malicious code is also programmed to modify infected computers' Master Boot Records. The change renders computers inoperable following any attempt to reboot.

The impact of this self-destruct sequence should be minimal, however. Weafer said that he expects only a few thousand machines will be damaged. "I don't expect this to be a major issue, except perhaps in South Korea," he said.

The cyber attack against sites in the U.S. and South Korea began on July 4 and temporarily interfered with access to the Web sites of the Treasury Department, the Transportation Department and the Federal Trade Commission.

The South Korean Intelligence Service estimated that about 20,000 compromised computers -- mostly in South Korea -- had been ordered to conduct a Distributed Denial of Service (DDoS) attack on U.S. and South Korean sites.

Given the timing, which coincided with a North Korean missile test, suspicions have been raised about the involvement of hackers in North Korea or possibly China.

In a press briefing yesterday, State Department spokesman Ian Kelly said, "[The attacks] are continuing, and we are taking measures to deal with this and any potential new attacks." He said he had no information about whether North Korea was involved.

It is possible to direct an attack of this sort from anywhere. According to Alan Paller, research director at The SANS Institute, the compromised computers participating in this attack are located all over the world, including the U.S. The bots that participate also vary over time, so that the source of the attack is constantly changing.

"The attacks have become increasingly sophisticated since the end of last week -- it started as a flood that was easy for network service providers to filter and then went through at least two increases in sophistication so that the flood looks more and more like legitimate traffic," said Paller in an e-mail. "Network providers have to work much harder to filter out malicious traffic that resembles legitimate traffic."

But with W32.Dozer already deleting files and crippling its hosts, the attacks should soon subside.