According to security firm Sophos, 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.

A close second is Brazil with 11.1 percent followed by Turkey with 5.2 percent.

Surprisingly 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 in the same period.

Graham Cluley, senior technology consultant for Sophos, said: “If America could clean up its compromised PCs it would be a considerable benefit to everyone around the world who uses the net”.