The results show that anti-spam legislation recently enacted in the US has had little impact, said Sophos.
The Controlling the Assault of Non-Solicited Pornography and Marketing Act, or CAN-SPAM Act, which came into force on 1st January 2004, established a framework of administrative, civil, and criminal tools to tackle unsolicited commercial e-mail.
Despite it's name the CAN-SPAM Act fails to actually "can" spam. There is no ban on sending unsolicited commercial e-mail or text messages. Instead, it requires that spam sent to consumers includes a means of opting-out of the mailing list used by the sender.
Critics have accused the Act of being narrow and weak, accusations that are difficult to deny in the face of the US's current standing as the producer of 42.53% of all spam, according to Sophos.
South Korea, the most broadband connected country in the world, is second in the league table, exporting 15.42% of all spam, says the report. China and Hong Kong rank third, being responsible for 11.62% of all spam, and Brazil is fourth, with 6.17% of all spam originating from its shores. The UK, which lies tenth in the table, is responsible for only 1.15% of all spam.
"Spammers are motivated by watching their bank accounts get fatter and fatter, and many have turned to hacking into innocent third-party computers to send their junk e-mails," warned Cluley. "Many of the computers sending out spam are likely to have had their broadband internet connections exploited by remote hackers."
"Zombie computers - PCs which have been compromised by hackers or virus writers - are sending out approximately 40% of the world's spam, all without the apparent knowledge of the user," he added.