Spam drops as Rustock, other botnets go quiet

The infamous Rustock botnet, responsible for almost half of all spam sent last year through its command-and-control system exploiting over a million compromised PCs, has suddenly slowed to a crawl, revealed Symantec.

The security firm also said the unexplained event has led to a substantial drop in spam. One of the oldest and most successful spam-producing botnets, Rustock typically would send about 44.1 billion spams per day but that volume suddenly dropped on December 25 to about 500 million per day, according to Symantec.

There's no clear explanation for the decrease, which may be temporary, says Paul Wood, senior analyst with Symantec hosted services. But he notes that the website for the Rustock spam-promoting affiliate organisation called SPAMIT was shut down last October. To add to the mystery, other spam-producing botnets are suddenly going silent, including one called Lethic on December 28 and Xarvester on December 31.