The United States was the 800-pound spam-spewing gorilla throughout 2004, a spot it held from wire to wire throughout the year, an anti-virus firm announced Monday.

According to researchers at U.K.-headquartered Sophos, the U.S. accounted for 42.1 percent of the world's spam, more than three times the next-guiltiest nation, South Korea, which launched 13.4 percent of the globe's junk mail. China, Canada, and Brazil rounded out the top five.

"When we first reported on the top spamming countries back in February 2004, the U.S. had the excuse that the CAN-SPAM Act had been in existence for a couple of months," said Graham Cluley, a senior technology consultant for Sophos, in a statement. "Almost a year and millions of spam messages later, it's quite evident that that the CAN-SPAM legislation has made very little headway in damming the flood of spam."

Sophos, which used its global network of spam honeypots to attract messages to analyze, also noted that countries with high numbers of broadband Internet users are attractive targets to spammers, who often hijack vulnerable PCs, then turn them into spam "zombies" to disguise the real origin of the junk mail.

South Korea, which boasts the world's highest percentage of Internet users that connect via always-on, fast broadband links, is in second place on Sophos' list for that very reason.

"Spammers are motivated by one thing: fast and easy money," said Cluley. "Many home users' computers are sending out spam because they have had their broadband internet connections exploited by remote hackers. Zombies are sending out over 40% of the world's spam, usually to the complete ignorance of the PC's owner."