DDoS malware comes with self-destruct payload

How to kill a zombie

Attacks that have wreaked havoc on dozens of South Korean government websites over the past week have included another nasty surprise: a malicious payload the causes the infected machines recruited to carry out the assaults to spontaneously self-destruct.

The DDoS, or distributed denial-of-service, attacks were first spotted on Friday hitting websites including South Korea's president, National Intelligence Service, and Foreign Ministry. They were unremarkable except for a couple details ferreted out by McAfee security researcher Georg Wicherski. The most striking: The infected zombies used in the attacks are programmed to destroy sensitive system files, a blow that can incapacitate the machines.

“One thing is clear,” Wicherski wrote in a blog post published earlier this week. “This is a serious piece of malware. It uses resilience techniques to avoid a takedown and even has destructive capabilities in its payload.”

“Resilience techniques” is a reference to a multi-stage command-and-control structure, which spreads the malicious instructions into two layers to make it harder for whitehats to reverse engineer the system. The first stage contains little more than an encrypted list of servers to a second set of C&C machines, which issue the attack commands.

What's more, the first layer of servers are physically distributed in dozens of countries, providing backup in the event some of them are taken down.

Once the infected bots reach the second stage, they receive the list of sites to attack. But they also receive commands to self-destruct by overwriting the master boot record of their primary hard drive.

“If you want to destroy all the data on a computer and potentially render it unusable, this is how you would do it,” Wicherski said.

The bot malware also instructs the machine to overwrite a variety of other files stored on the hard drive, including those used for Microsoft Office documents and files used by programming languages such as C, C++, and Java.

Botmasters have some flexibility about when the self-destruct mechanism is triggered, but the number of days is limited to 10. Resetting the zombie's date to to a time before it was infected will activate the overwrite sequence immediately.

More from Wicherski is here.. ®

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