The UK has dropped two places in the league of the world's top spam-producing countries,

Now in 12th place, the UK produced 2.5 per cent of the world's junk email in the last three months of 2007, says research from security software firm Sophos.

The US continues to be the world's largest producer of spam, with a 21.3 per cent share, while Russia has risen from fourth to second place, with a score of 8.3 per cent.

"Responsible for a third of all unwanted email, USA and Russia can be viewed as the two dirty men of the spam generation, polluting email traffic with unwanted and potentially malicious messages," said Sohpos security consultant Carole Theriault.

"It is not the case that a third of the world's spammers are based in those countries, but that legions of computers are poorly defended, allowing hackers to break in and turn them into botnets for the spreading of spam and malware."

China is third in the league with a 4.2 per cent share.