Cybercriminals have hijacked nearly 12 million new IP addresses since January, a 50% increase since 2008, McAffee said.
The US now houses the largest percentage of botnet-infected computers, hosting 18% of all so-called "zombie" machines. China is in second place with around 13%.
Criminal syndicates are attempting to rebuild in the wake of the November 2008 take-down of notorious spam hosting domain McColo, McAffee said. Spam volumes have already recovered 70% since the takedown.
"The massive expansion of these botnets provides cybercriminals with the infrastructure they need to flood the Web with malware," said Jeff Green, senior vice president of McAfee Avert Labs. "Essentially, this is cybercrime enablement."
Despite the hype surrounding Conficker, the worm is responsible for only a small subset of all threat reports, Green added. The Conficker-spread Autorun malware represented only 10% of all detections reported in Q1.
The Koobface virus has also made a resurgence, with McAffee detecting 800 new variants in March alone, Green said.