The malware state of the art continues to improve. In particular, the latest version of the TDL rootkit family--aka Olmarik, TDSS, Alureon--contains sophisticated mechanisms for bypassing security features built into 64-bit versions of Microsoft Windows Vista and Windows 7, and can download additional, standalone malware applications.

The fourth version of the TDL malware first appeared in August 2010 and contained sophisticated new techniques for defeating security measures. "The most radical were those made to its mechanisms for self-embedding into the system and surviving reboot," said Aleksandr Matrosov, a senior malware researcher at ESET, in an analysis of TDL4 published by Infosec Institute.

For example, TDL4 can "load its kernel-mode driver on systems with an enforced kernel-mode code signing policy," meaning the 64-bit versions of Vista and Windows 7. At that point, the malware can hook directly into the Windows operating system, even with "kernel-mode patch protection policy enabled," he said. "This makes TDL4 a powerful weapon in the hands of cybercriminals."

That, of course, is the point. "Modern malware authors are businessmen," said Jack Koziol, security program manager at Infosec Institute. Accordingly, they've only started to target x64--aka 64-bit--operating systems since their use has become more widespread. "We have just started to see consumer software that leverages x64 architecture in a widespread fashion in the last year or so," he said in an email interview.

Building a botnet that reliably exploits 64-bit systems takes talent. "This is not something your average programmer could do in a weekend, this is some serious heavy lifting done by a programmer with deep knowledge of x64 Windows 7 operating system internals," said Koziol. "TDSS is also very reliable, so we have to assume there was a definite [quality assurance] process in place here, with various testing versions."

How does TDL4 generate money for its operators? An ESET analysis of TDL3 traced the botnet's operators to a cybercrime group known as DogmaMillions, who used a pay-per-install model. Anyone who licensed the malware received a unique username and log-in, as well as a personal customer service contact. Every time they installed the malware, software built into the executable would alert the distributor that it had been installed, so the customer could be billed.

DogmaMillions shuttered in the fall of 2010, said Matrosov, presumably because it was attracting too much attention--especially as major affiliates reported making up to $100,000 per day using the TDL3. But at the end of 2010, another group--with a very similar advertising campaign and business model--appeared, named GanstaBucks.

Since the fourth version of TDL first appeared, it's undergone numerous, incremental revisions. For example, in March 2011, a new version of TDL4 appeared that--after infecting a PC--installs the standalone Glupteba.D malware, which can then download and execute other pieces of malware. According to Matrosov, the malware "uses the customary blackhat SEO [search engine optimization] methods to push clickjacking contextual advertising as used," specifically for the Begun advertising network, which is big in Russia.

What's the big takeaway from the TDL4 teardown? First, that no matter the security defense, such as driver signing, a way to defeat it can be found. "TDSS is another example that proves the rule that no matter whatever security precautions are in place, the bad guys will overcome them," said Koziol.

Another finding is that criminals don't always go for the biggest bucks. "Malware that is too aggressive in monetizing the infected install base, such as Coreflood, will attract the attention of federal and international law enforcement," said Koziol. "Something like TDSS that doesn't hijack banking information but simply performs clickfraud is more likely to stay under the radar of the big law enforcement guns out there."