Researchers at rival -- now part of Symantec Corp. -- see the situation differently.

According to Matt Sergeant, a senior anti-spam technologist at the company, spam levels have bounced back to about two-thirds of what they were before McColo was yanked off the Internet. In fact, spam jumped to that volume only today.

Sergeant wasn't surprised by the lag time between McColo's shutdown and a return of spam. "The Asprox and Rustock botnets are back with a vengeance after having found new command and control [servers]," Sergeant said in an e-mail. "Cutwail never went away and it seems its owners have used the opportunity to increase output. Mega-D is also on the rise again."

Sergeant and Edwards, however, agreed on one thing: The Srizbi botnet looks gone for good.

"Srizbi, having once been responsible for 50% of all spam, is now completely defunct," said Sergeant, who added that sans that botnet, "spam levels won't return to what they had been."