To reach the one or two messages that are actually of interest, you have to wade through a minefield of offers for loans, pills, investment opportunities in dodgy African companies and the chance to become friends with Eastern European women, who all appear to have graduated from the same school of comedy English.

These unsolicited emails, otherwise known as spam, have become a modern scourge. But as well as wasting our time and potentially infecting our computers with online viruses,
it seems they're also harming the environment.

According to new research, carried out for computer protection company McAfee, spam emails produce as much greenhouse gas emissions each year as 3.1 million cars. The study showed that globally, spam uses 33 billion kilowatt hours (KWh) a year – enough energy to power 2.4 million homes. It also found that the UK was the joint fourth biggest emitter of CO2 from spam in the world, creating 50,000 tonnes of carbon dioxide a year. In other words, we're paying a high environmental price for the time we spend trying to filter out these unwanted emails.

Jeff Green, senior vice president of McAfee Avert Labs, says the study shows that spam has an impact on all our
lives. "Stopping spam at its source, as well as investing in state-of-the-art spam filtering technology, will save time and money and will pay dividends to the planet by reducing carbon emissions
as well."

However, this is easier said than done. Back in 2004, Bill Gates told the world that "spam will soon be a thing of the past". The computer supremo confidently predicted that unwanted emails would be stamped out within a couple
of years. When he made his prediction, spam accounted for around half the global emails sent. Now that figure is more than 80 per cent, and rising.

It's estimated there are now a staggering 60 billion junk emails sent every day and David Lacey, an online security expert, claims that governments, internet authorities and service providers aren't doing enough to tackle
the problem.

"Unfortunately, the standards for managing the internet aren't very rigorous. There are things that could be done and if there was concerted action then we have the technology to stop some of these spam operators, but there isn't the appetite for it."

Other solutions that have been discussed include limiting the number of emails that can be sent from a PC and the introduction of an electronic equivalent of a stamp, which would force the sender to pay up if an email was rejected as spam. But so far these have proved difficult to implement.

The rise in spam has been fuelled by criminal gangs targeting people's emails, rather than exploiting weaknesses in computer software.

"There's big money in it and they have professional software people working for them, so
we're not talking about a small- scale threat. They constantly change their addresses to disguise where the spam is coming from and they're coming up with new ways of infiltrating PCs so they stay one step ahead," says Mr Lacey.

Although these messages – known as phishing emails – tend to be relatively easy to spot, increasingly sophisticated malware (malicious software), which can infiltrate a computer system without the owner's knowledge, is being used to take over millions of PCs to create what are called botnets – a network of PCs – that are then used to fire out millions of spam emails. "They target vulnerable computers, those that don't have the latest anti-virus software, and they spread from there," says Mr Lacey.

It's estimated that as many as one in 10 computers worldwide may now be compromised and one in 10 web pages "booby trapped".

"If the levels of spam continue to increase at this rate then people may become too frightened to click on a banner, or an advert, and this could undermine the entire commercial business of the internet."

The best advice for ordinary PC users is to delete any suspicious looking emails without opening them and keep anti-virus software up to date. But don't expect magic solutions any time soon.

"People like Bill Gates have been trying to solve this problem for years and nobody's cracked it. There's no indication that this will go away so we're going to have to live with it for a long time."