WASHINGTON - The United States and China host nearly two-thirds of spam, viruses and other computer security threats delivered around the world in 2006.

Computer security firm Sophos said 34.2 percent of the so-called malware last year originated from the United States, with 31 percent from China. Russia was third, accounting for 9.5 percent of the threats.

"The enormous number of computers based in North America probably makes it no surprise that the US heads the list, and is hosting over a third of all websites containing malicious code," the report said Monday.

Sophos said it identified 207,684 different threats, ranging from spam, viruses and "trojans" that download programs to infect computers, to "ransomware" designed to "kidnap" data by encrypting it, and provide the password once a ransom has been paid.

The report said 90 percent of all spam is now relayed from "zombie computers" infected with some kind of malicious code.

Sophos said its "dirty dozen" list of worst spam-relaying nations was again headed by the United States, accounting 22 percent of the spam sent worldwide.

China was second with 15.9 percent, followed by South Korea (7.4 percent), France (5.4 percent), Spain (5.1 percent), Poland (4.5 percent), Brazil (3.5 percent), Italy (3.2 percent), Germany (3.0 percent), Britain (1.9 percent) and Russia and Taiwan (each with 1.8 percent).

Sophos noted however that because spam is mostly relayed from zombie computers, the relaying PC does not need to be based in the same country as the computers being used to send the spam.

Sophos predicts that 2007 is likely to see a significant shift away from the use of e-mail security threats, with cyber criminals instead looking to infect computers through contaminated websites.

"The number of websites being infected with malware is on the rise," the report said. "SophosLabs is currently uncovering an average of 5,000 new URLs hosting malicious code each day."