"Frank Boldewin had seen a lot of malicious software in his time, but never anything like Rustock.C. Used to infect Windows PCs and turn them into unwitting spam servers, Rustock.C is a rootkit that installs itself on the Windows operating system and then uses a variety of sophisticated techniques that make it nearly impossible to detect or even analyze.
When he first started looking at the code earlier this year, it would simply cause his computer to crash. There was driver level encryption, which had to be decrypted, and it was written in assembly language, using "spaghetti code structure" that made it extremely hard for Boldewin to figure out what the software was actually doing. " – Content courtesy of A sneaky security problem, ignored by the bad guys – Network World