SophosLabs scanned all spam messages received in the company's global network of spam traps, and has revealed that the U.S. struggles to significantly reduce its level of relayed spam, with more than a fifth (21.6 percent) of the world's spam originating from there.

Sophos believes that a possible reason for the U.S.' increasing lead in relayed spam when compared to its closest rival, China, is the emergence of over 300 strains of the mass-spammed Stratio worm. The worm, also known as Stration or Warezov, uses a trick dependent on the victim being able to speak English in its attempt to convert innocent PCs into members of a spam botnet.

The top twelve spam-relaying countries are as follows: