Beware zombies attacking you with spam. No, it’s not some bizarre Monty Python sketch, but a warning of a coming plague. Colin Wells from Exeter receives a staggering 44,000 junk (or spam) e-mails every day, making him the most spammed person in Britain, according to a UK-based antispam software company.

Wells doesn’t even work in a hi-tech industry - he’s a foreman for Stagecoach buses. One mistake he made was to e-mail the spammers in an attempt to unsubscribe. “For a couple of months I was clicking a link to stop them resending, but I found out this confirms the e-mail address as active. From then on, the amount of spam I was getting was doubling every couple of months.”

It’s a problem that’s worsening - but why? Back in 2004 Bill Gates predicted the end of spam within just two years. Instead Wells is racking up 16m junk messages a year. Spam now accounts for more than 80% of all e-mail traffic, by some industry estimates.

The problem is largely due to so-called “zombie” computers - home PCs that have been infected by a virus ( often contracted from an e-mail attachment) and are sending reams of spam without their owners’ knowledge. The criminal gangs that control the zombies use them to fire off thousands of messages offering porn, attempting financial fraud and of course selling Viagra. Worse still, many gangs also gather e-mail contacts lists from zombie computers, ensuring the owners’ families and friends are deluged with spam.

“We live in a very interconnected world,” says Con Mallon of Symantec, an American security software company. “Spammers are moving tactics all the time. It can take days or weeks to change our filters, giving time for spam to build a lot of momentum. For the bad guys it’s a numbers game.”

And those numbers are terrifying. Commtouch, an Israeli antispam company, estimates there are at least 10m zombie computers active worldwide. Although many spammers target richer, developed nations, it’s countries that can’t afford the latest security technologies that tend to suffer the worst zombie infestations. Turkey alone houses an estimated 1m compromised computers, with Brazil and India not far behind.

Dave Rand of Trend Micro, a company that makes antivirus software, lays the blame at the doors of internet service providers (ISPs). “ISPs need to take a more active stance at protecting their customers,” he says. “They should tell customers when their computers are exhibiting signs of being compromised. Most ISPs today choose to ignore the problem.”

The rules for preventing your computer becoming a spam zombie are the same as avoiding viruses: don’t open e-mail attachments unless you’re certain of their origin and keep your security up to date. Another golden rule is not to reply to any spam, no matter how tempting the offer. Or you can do what Colin Wells did - spend extra on specialised antispam software. His Clear-MyMail service costs £18 a year, but Nucleus Research, the American hi-tech analysts, estimates that the time wasted dealing with spam costs businesses more than £350 a year per employee.

Bill Gates’s rosy predictions notwithstanding, spam is going to get worse. “Unless we do something, at some point people will give up on e-mail as a communication medium,” says Rand.

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