According to U.K.-based Sophos, U.S. senders accounted for 23.1 percent of the world's spam in 2006's first three months. Chinese spammers sent 21.9 percent of global junk mail during the same period.
Laws such as the CAN-SPAM Act, and resulting prosecutions, have reduced the U.S.'s share of spam, said Sophos senior technology consultant Graham Cluley in a statement.
"Two years ago, the U.S. accounted for over half of all spam sent to the world…now it is less than a quarter, evidence which confirms that more Americans are waking up to the need to protect their computers," Cluley said.
Other countries in Sophos' top 10 spammers include South Korea, France, Poland, Spain, Germany, Brazil, Japan, and the U.K.
Broken down by continents, however, Asia continues to beat all comers in the spam ring; in the first quarter, Asia accounted for 42.8 percent, while North America spammed 25.6 percent of the world's unwanted messages.
Although the spam burden may have shifted, the volume of spam has not fallen. E-mail filtering and security service provider MessageLabs, for example, recently noted that the world-wide ratio of spam to all mail actually climbed by 0.7 percent in April to 58.5 percent.