Gone from the landscape, said , director of research at Atlanta-based , are "Srizbi" and "Storm," the botnets Stewart ranked as No. 1 and No. 5, respectively, in an .

Srizbi, and to a lesser degree "Rustock," were crippled two months ago when McColo Corp., a company that has long been hosting botnet command-and-control servers, was cut off from the Internet by its upstream providers after researchers accused it of harboring cyber-crime activity. Stewart was one of the researchers who had beaten the McColo drum.

When McColo's connection to the Internet was severed, as spammers were unable to use Srizbi or Rustock bots to send their junk mail.

But the relief was short-lived. "There was a time when the bot numbers were diminishing, and we made up some ground," acknowledged Joe Stewart, director of research at Atlanta-based SecureWorks Inc. Now, however, other botnets have come into prominence. Some of them were well-known before the McColo take-down, but had been relatively small, while others have come out of obscurity.

The result? "Spam isn't quite up to the pre-McColo level, but it's easily within the 80% to 90% range," said Stewart, citing numbers consistent with other estimates. , for example, estimated this month's spam level at 80% of that before the McColo shut-down.