Botnets Resurge After Holiday Break

File under "suspicious": Two seemingly unrelated botnets went dark for about a week, then suddenly reappeared, pushing updated malware to infected PCs and unleashing a massive spam campaign. Substantial numbers of the spam messages are emanating from the .ru domain, which is Russia's top-level domain.

One of the botnets in question is Waledac, aka Storm, which recently distributed an update to all infected computers, generated large quantities of spam with a New Year's theme, then went dark in early January. About a week later, however, the botnet resurfaced, unleashing a new "magic blue pill" spam campaign, as it's done in the past.

The new Waledac malware also received a 2011 makeover. "After the downtime, the botnet came back up and an update followed. The binary executable of the bot was updated, the code itself showed small changes, and the network messages exchanged by the botnet peers showed a new message containing a spam job involving pharmaceutical spam, rather than misleading applications," according to a blog post from Symantec's Andrea Lelli.

"The spammed links will redirect the user on a domain controlled by the botnet, which in turn is a redirector to a domain owned by the 'Trusted Tabs' branding, a notorious pharmaceutical spam operation group," she said.

Interestingly, at about the same time that Waledac reappeared, Rustock -- the world's most prolific botnet in 2010, in a year that saw new malware volume reach an all-time high -- also resurfaced, and likewise began issuing large quantities of pharmaceutical spam.

The timing of the two botnets resurfacing is "a suspicious coincidence indeed," said Lelli, though she cautioned that Symantec was still investigating whether the two botnets were, in fact, controlled by the same group. On the upside, the two botnets' spam volumes are currently lower than in 2010.