Security firm Sophos has released its latest top 12 list of the worst countries for relaying spam.
The US came top in Sophos' 'dirty dozen', relaying over 13 per cent of all spam and accounting for "hundreds of millions of junk messages every day". India came second at just over seven per cent, followed by Brazil at just under six per cent.
Most surprising is China. Usually blamed for many of the world's internet problems, it did not make the top 12 list, coming in at 15th with under two per cent of all spam.
The UK is at joint ninth with Russia and Italy, and follows South Korea in fourth place, Vietnam in fifth place and Germany in sixth place.
"All eyes aren't so much on which countries are on the list, but the one which isn't. China has earned itself a bad reputation in many country's eyes for being the launch pad of targeted attacks against foreign companies and government networks, but at least in the last 12 months they can demonstrate that the proportion of spam relayed by their computers has steadily reduced," said Graham Cluley, senior technology consultant at Sophos, in a blog post.
"A new dirty 'gang of four' - South Korea, Brazil, India and their ringleader the US - account for over 30 per cent of all the spam relayed by hacked computers around the globe."
Sophos said that spam accounts for 97 per cent of all mail aimed at business mail servers, and wastes productivity, time and resources.
Cluley added that, in some cases, companies are unwittingly opening themselves up to explotiation and manipulation.
"Countries such as the US would do well to remember that cleaning up infected PCs in their own back yard will be an important step in fighting cyber crime," he said.
"Furthermore, we all shouldn't forget that if no-one bought products sold via spam there would be a lot less incentive to send junk email.
"Computer users should not just protect their computers from threats like malware and spam, they should also pledge to never ever buy anything advertised via spam."