The proliferation of temporary websites being set up by criminals is a growing threat, according to web security firm MessageLabs.
"Disposable domains are becoming a larger problem via a tactic known as 'domain kiting' in which cyber-criminals acquire domains without paying for them and use them for illegal gains," said Mark Sunner, chief technology officer at MessageLabs.
Domain kiting registrars create small websites crammed with links using domain names for which they do not pay. They generate money when innocent surfers land on the page and click on the links. The scam takes advantage of the domain name system's five-day refund period.
Despite this practice, the monthly MessageLabs Intelligence Report found that the overall threat levels for May remained relatively stable.
Malaysia saw the largest increase in virus attacks during the month, with one in 15 emails carrying a piece of malware. But the worst hit country was still India, which saw one in 9.6 emails infected with a virus.
Hong Kong and Israel were the most spammed countries, with junk mail levels running at 64 per cent.
Sunner explained that the spam threat is now worse because the technology to take control of users' PCs had moved on.
"Cyber-criminals have become more adept at harvesting infected computer address books and using simple techniques to amplify their reach," he said.
"This has turned the traditional botnet or zombie into a virtual spam cannon capable of blasting out millions of emails a day."
MessageLabs found that the global ratio of spam in email traffic in May from new and unknown bad sources was 57.9 per cent. This translated as one in 1.7 emails and is an increase of 0.6 per cent from April.
Meanwhile, the global ratio of viruses in email traffic from new sources was one in every 67.1 emails, a decrease of 0.3 per cent from April's figures.
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