From Kelly Jackson Higgins’ “The World’s Biggest Botnets” (Dark Reading: 9 November 2007):
You know about the Storm Trojan, which is spread by the world’s largest botnet. But what you may not know is there’s now a new peer-to-peer based botnet emerging that could blow Storm away.
“We’re investigating a new peer-to-peer botnet that may wind up rivaling Storm in size and sophistication,” says Tripp Cox, vice president of engineering for startup Damballa, which tracks botnet command and control infrastructures. “We can’t say much more about it, but we can tell it’s distinct from Storm.”
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Researchers estimate that there are thousands of botnets in operation today, but only a handful stand out by their sheer size and pervasiveness. Although size gives a botnet muscle and breadth, it can also make it too conspicuous, which is why botnets like Storm fluctuate in size and are constantly finding new ways to cover their tracks to avoid detection. Researchers have different head counts for different botnets, with Storm by far the largest (for now, anyway).
Damballa says its top three botnets are Storm, with 230,000 active members per 24 hour period; Rbot, an IRC-based botnet with 40,000 active members per 24 hour period; and Bobax, an HTTP-based botnet with 24,000 active members per 24 hour period, according to the company.
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1. Storm
Size: 230,000 active members per 24 hour period
Type: peer-to-peer
Purpose: Spam, DDOS
Malware: Trojan.Peacomm (aka Nuwar)
Few researchers can agree on Storm’s actual size — while Damballa says its over 200,000 bots, Trend Micro says its more like 40,000 to 100,000 today. But all researchers say that Storm is a whole new brand of botnet. First, it uses encrypted decentralized, peer-to-peer communication, unlike the traditional centralized IRC model. That makes it tough to kill because you can’t necessarily shut down its command and control machines. And intercepting Storm’s traffic requires cracking the encrypted data.
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Storm also uses fast-flux, a round-robin method where infected bot machines (typically home computers) serve as proxies or hosts for malicious Websites. These are constantly rotated, changing their DNS records to prevent their discovery by researchers, ISPs, or law enforcement. And researchers say it’s tough to tell how the command and control communication structure is set up behind the P2P botnet. “Nobody knows how the mother ships are generating their C&C,” Trend Micro’s Ferguson says.
Storm uses a complex combination of malware called Peacomm that includes a worm, rootkit, spam relay, and Trojan.
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But researchers don’t know — or can’t say — who exactly is behind Storm, except that it’s likely a fairly small, tightly knit group with a clear business plan. “All roads lead back to Russia,” Trend Micro’s Ferguson says.
“Storm is only thing now that keeps me awake at night and busy,” he says. “It’s professionalized crimeware… They have young, talented programmers apparently. And they write tools to do administrative [tracking], as well as writing cryptographic routines… and another will handle social engineering, and another will write the Trojan downloader, and another is writing the rootkit.”
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Rbot
Size: 40,000 active members per 24 hour period
Type: IRC
Purpose: DDOS, spam, malicious operations
Malware: Windows worm
Rbot is basically an old-school IRC botnet that uses the Rbot malware kit. It isn’t likely to ever reach Storm size because IRC botnets just can’t scale accordingly. “An IRC server has to be a beefy machine to support anything anywhere close to the size of Peacomm/Storm,” Damballa’s Cox says.
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It can disable antivirus software, too. Rbot’s underlying malware uses a backdoor to gain control of the infected machine, installing keyloggers, viruses, and even stealing files from the machine, as well as the usual spam and DDOS attacks.
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Bobax
Size: 24,000 active members per 24 hour period
Type: HTTP
Purpose: Spam
Malware: Mass-mailing worm
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Bobax is specifically for spamming, Cox says, and uses the stealthier HTTP for sending instructions to its bots on who and what to spam. …
According to Symantec, Bobax bores open a back door and downloads files onto the infected machine, and lowers its security settings. It spreads via a buffer overflow vulnerability in Windows, and inserts the spam code into the IE browser so that each time the browser runs, the virus is activated. And Bobax also does some reconnaissance to ensure that its spam runs are efficient: It can do bandwidth and network analysis to determine just how much spam it can send, according to Damballa. “Thus [they] are able to tailor their spamming so as not to tax the network, which helps them avoid detection,” according to company research.
Even more frightening, though, is that some Bobax variants can block access to antivirus and security vendor Websites, a new trend in Website exploitation.