Spammers are increasingly using emails purporting to come from 'desperate housewives', but recipients clicking on the links are likely to get more than they bargained for. The emails link directly to pornographic websites, where visitors run the risk of picking up a nasty dose of spyware.

This trick is one of the latest additions to the spammers' armoury, and has led to a jump of 180 per cent in sex-related spam over the past month.

Clearswift's Spam Index, the most in-depth monthly study of individual unsolicited emails, reported a rise from 10 per cent to 18 per cent of the total analysed.

According to the content security company, the number of spam emails linking to these sites, which initially appear to be dating forums for swingers, is rocketing.

However, the firm warned that closer inspection reveals that they are actually a front for porn sites hosted in Russia and China.

Alyn Hockey, Clearswift's director of research, said: "Aside from the fact that these emails are bogus, clicking on any link within a spam mail can lead to a whole host of unwanted problems.

"They frequently contain malicious programs including spyware or rogue internet diallers which can run up huge unexpected bills."

Hockey added that, over the past 20 months, there has been a variety of spins on the sex spam theme in order to attract punters to porn websites, ranging from offers of a well-paid career as a porn star, to actually setting up and running a porn website.

According to Clearswift's spam analysis, the incredible array of bizarre products seen after Christmas - including a dog-translator and a device which turns a coffee table into a kennel - has completely dried up.

In contrast, the percentage of spam in the "direct products" category remained steady over the past month, declining slightly from 17.85 per cent to 14.47 per cent.

Yet the diversity has gone, with software now accounting for over three-quarters of products on offer and 12.03 per cent of spam overall.

Interestingly, a Rolex is no longer flavour of the month. The luxury watch offers which plagued inboxes towards the end of 2004 have vanished. After peaking in October, they remained consistent in November, and have since slid into obscurity. One new arrival, however, is fraudulent Sony PSP giveaways.