About 30 per cent of internet users have bought goods advertised in spam emails, research from internet security vendor Marshal has found.

Marshal polled 622 internet users, of which 29.1 per cent admitted to having purchased items through links in spam emails. The most frequently ordered items were sexual enhancement pills, adult entertainment, software and luxury items including watches, jewellery and clothing.

A report from Forrester Research in 2004 demonstrated that one fifth of internet users had bought products through spam. Marshal's vice president of products, Bradley Anstis, claimed that spam response rates were considerably higher than people realised.

Anstis indicated that, although estimates place the number of purchases from spam as less than ten in ten million, the majority of spam is blocked by filters, meaning actual response rates are much higher. He said: "Many of us often question ourselves: why is there so much spam? The answer is enough people are purchasing products from spam to make it a worthwhile and profitable endeavour for spammers.”

“Industry estimates vary, but the consensus is that more than 150 billion spam messages circulate daily and regularly account for more than 85 per cent of all emails. The problem is enormous and it is only getting worse. Spam consumes bandwidth and resources, costs recipients time and money and it has become one of the Internet’s biggest security problems now that spammers have turned their hand to distributing malware as well.”

Anstis revealed that the advent of botnets, which are remotely controlled networks of thousands of infected PCs, has been a boon for the spam industry. Spammers are now able to charge as little as $5 (£2.68) to send a million spam messages. He said: “A common misconception is that ‘regular’ people do not buy from spam. But, you have to consider the types of products people are buying. It is pirated software, knock-off watches, counterfeit designer goods, cheap drugs and prescription medicines, pornography and other adult material.

"The Internet provides convenience and a degree of anonymity to people who want to buy illegal or restricted goods. It is a black market and spam has become a conventional means of advertising to a willing audience of millions of people who are purchasing from spam.”