Digital Trends - The shady world of botnets and malware distribution is always full of surprises, and few of them are pleasant. However, a recent development might just fall into that category: security researchers have noted that the command-and-control servers that manage the infamous Rustock botnet have gone offline. Rustock is one of the largest sources of email spam on the Internet, and its newfound silence has created a significant decline in the amount of spam in circulation. Some estimates have says Rustock is responsible for as much as 40 percent of the world’s spam.