Unwanted e-mail filled in-boxes by the billions in 2003, as legal and technical efforts to stop the deluge were ineffective.

For the first time, the amount of unsolicited commercial e-mail that was sent surpassed the number of legitimate messages. Unwitting PC users played a part in mass mailings, too, as the majority of all spam was sent through hijacked computers via open relays, according to antispam company MessageLabs.

Virus and spam techniques merged this year to pose a malicious and potent threat to corporations and network administrators. Viruses disguised as legitimate e-mail infected many computers with programs designed to overtake the PC and propagate throughout a network by way of mass mailings. SoBig.F was the worst mass-mailing virus ever recorded and the biggest example of such a spam virus. "Swen.A," "Klez.H" and "Sysbug" reaped havoc in a similar way. Spammers are now also attacking antispam activists with viruses such as the latest two Mimail variants.

Antispam features also became must-haves for most firewall and e-mail gateway products. Many antispam and security companies merged or partnered in their efforts to battle the scourge, and more consolidation is expected in 2004. Microsoft founder Bill Gates even promised new technology breakthroughs in security and spam-fighting mechanisms.

Internet service providers, federal regulators and state attorneys cracked down on spammers like never before. The Federal Trade Commission asked Congress for sweeping new powers to cooperate closely with governments abroad and prosecute domestic and overseas spammers more readily. Federal and state law enforcement agencies pledged to take an aggressive new approach to fighting spam by identifying and closing open-relay mail servers around the world. Microsoft, EarthLink and Amazon.com filed numerous lawsuits against suspected spammers.

Researchers also proposed e-mail verification systems to thwart spam, while industry groups formed new relationships to find solutions. Marketers, meanwhile, fought for their right to send legitimate e-mail to consumers. For example, Yahoo changed its privacy policy to allow itself new marketing liberties with consumers.

Congress passed the first federal antispam bill, capping more than six years of failed congressional attempts to enact a federal law. Set to go into effect early in 2004, the law would preempt more stringent state legislation like California's, which had been criticized. The popularity of the National Do Not Call Registry also fueled demand for a similar registry for unsolicited commercial e-mail, which became a tenet of the new law. But telemarketers are concerned that it will limit free speech and hamper e-commerce.

--Stefanie Olsen