According to Denver-based MX Logic, 56 percent of the spam it tracked during July was sent by zombies infected with a malicious Trojan horse and transformed into a spam-spewing monster. That's down from June's 62 percent, but up slightly from May's 55 percent.
"Hijacked PCs have become not only the preferred distribution tool for spammers, but also a primary source of Internet pollution," said Scott Chasin, the chief technology officer at MX Logic, in a statement.
MX Logic also said that the percentage of unsolicited commercial e-mail complying with the federal anti-spam CAN SPAM Act ticked up a bit in July. Last month, 4 percent of all unsolicited mail met the law's requirements; in June, that figure was 3 percent, also the average since Can Spam went into effect in January 2004.