The US has been named the world's biggest spam-producing country.
Security firm Sophos said the US was responsible for 15.6 percent of all spam received between April and June this year - that's one in every six junk emails.
The US was closely followed by Brazil, which produced 11.1 percent of all spam, and Turkey, which generated 5.2 percent.
Russia, which was second on Sophos' Dirty Dozen list a year ago, has now fallen to ninth place and was only responsible for 3.2 percent of all spam between April and June.
Graham Cluley, senior technology consultant for Sophos, said: "Barack Obama's recent speech on cybersecurity emphasised the threat posed by overseas criminals and enemy states, but these figures prove that there is a significant problem in his own back yard. If America could clean up its compromised PCs it would be a considerable benefit to everyone around the world who uses the net".
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