Although CAN-SPAM hasn't resulted in less spam, the law gives authorities a new tool in the fight against spam, Lochart said. "It's a good thing we have a law, so when we find some of these roaches, we can prosecute them," he said.

Spammers, apparently in response to CAN-SPAM, changed tactics this year, said Andrew Lochart, director of product marketing at Postini. More spammers are using so-called zombie networks -- computers hijacked with Trojan horse programs -- to send spam, and spammers are using increasingly sophisticated directory harvest attacks to spam corporate mail servers, he sai

CAN-SPAM also prohibits private citizens from suing spammers, instead allowing only state attorneys general or Internet service providers to file civil suits

Commtouch found that 80 percent of spam e-mail didn't include valid return e-mail addresses and more than 40 percent contained subject lines that weren't related to the text of the e-mail.

"There's been no reduction in the volume of spam," says Scott Chasin, MX Logic's chief technology officer. "In fact, the exact opposite--our spam rates are actually going up."

Less than 1 percent of spam e-mail sent to U.S. inboxes this month complies with a national antispam law that went into effect January 1, according to two spam filtering vendors.