The US remains the country responsible for relaying the most spam, says Sophos.

According to the Dirty Dozen list of the top 12 spam relaying countries from the security firm, the US was responsible for 11.3 percent of all spam sent during September this year. South Korea, which was previously at number seven in the list, now occupies the second position with 9.6 percent.

Sophos revealed that although the US remains the single worst offender, Asian nations now contribute a significantly higher proportion of global spam than for the same period in 2010, with Indonesia, Pakistan, Taiwan and Vietnam all joining the list since Q3 2010. In fact, as a continent Asia is responsible for more than half (50.1 percent) of all global spam, with Europe in second place with 21.4 percent and North America coming in third with 14.2 percent.

"The spam that attempts to smash its way into users' email accounts can vary from being annoying adverts to downright malicious attacks. In the worst cases, a spam message might be designed to infect your computer with a Trojan horse or phish your banking credentials," said Graham Cluley, senior technology consultant at Sophos.

"These latest statistics suggest that, as more people get online in Asia, they are not taking the right measures to protect their computers from infection, which results in the growth of botnets [networks of infected machines under the control of spammers]."

Sophos said PC users risk becoming part of botnets if they do not run up-to-date anti-virus software and the latest security patches. Typical methods of infection include clicking on links or attachments in spam messages.

"Don't ever be tempted to buy anything via spam, as that's what makes it worthwhile for commercial spammers," continued Cluley.

"The best way for individuals to send a message that spam will not be tolerated is to not buy, not try, not reply."