McAfee has posted a security warning about Apple iPhone ads. The post says "the scammers are up to their old tricks again". Potential purchasers are warned not to try and use a search engine to find a deal on the new gadget. That's after tests by the company's SiteAdvisor service found that submitting your email address to vendors meant hundreds of spam emails.

"Our inbox averaged 66 e-mails a week after signing up with easyfreecellphones.com. But our sign-up at giveawaycafe.com resulted in a stunning 511 e-mails per week," says researcher Shane Keats.

McAfee found these sites were experts in what it calls "bait and switch tactics".

Keats explains: "They seem to promise a free product, typically whatever is hot at the moment - this summer that means the Apple iPhone . The sites make it seem incredibly easy to win the free merchandise [by providing personal details].

"Few consumers are ever able to successfully complete all the requirements to actually get the free prize. Some sites even require the consumer to recruit five friends to complete offers. Industry insiders call it 'breakage' - this inability to jump through all the many hoops - and they take pride in their ability to break 95 per cent or more of the consumers who try."