Junk e-mails are one of the main causes of stress for office workers but few know what to do about it, says internet company Yahoo.
Ex-Eastender Dean Gaffney lends Yahoo a hand again junk e-mail
A poll of 1,000 computer users found that one in four had been fooled into opening unwanted messages believing them to be genuine.
On Thursday Yahoo launched a campaign to make people wary about what they open as part of a worldwide Dump The Junk Day, aimed at advising people never to reply to junk e-mails or forward them to friends.
John Webb, head of Yahoo Mail in the UK, said: "Our research shows that many British internet surfers don't have the knowledge to tackle junk mail effectively with over half of Britons actually helping to perpetuate the junk mail cycle."
An estimated 40% of e-mails sent worldwide are junk, costing firms huge amounts of money in delays and lost production.
Yahoo found that spam has become one of the most irritating aspects of working life in the UK.
94% of Britons find junk mail hugely annoying
56% unwittingly reply to spam
More than 25% had been fooled into opening spam
Only 2% have made a purchase in response to junk mail
Source: Yahoo survey
Junk e-mails ranked behind traffic jams and long working hours as causing stress for office workers.
But Yahoo found that many people are unknowingly making things worse by replying to the messages.
"Junk mail is effectively an intrusion of our privacy and one which many people lack the knowledge to protect themselves against," said Big Brother psychologist Professor Geoffrey Beattie.
"Whether the junk mail is coming into a personal or work e-mail inbox, unsurprisingly it leads to feelings of lacking control, frustration and anger."
The big internet service providers (ISP) all offer "anti-spam" programmes to weed out the unwanted mail.
Last week Microsoft said that it now blocked 2.4 billion junk messages to its MSN and Hotmail subscribers every day.
And AOL - the world's largest ISP - is suing more than 12 individuals and companies who are allegedly responsible for sending one billion unsolicited messages.
The company recently said it blocked about two billion junk messages in a single day, while last week Microsoft revealed its anti-spam measures now net about 2.4 billion spam e-mails sent to its Hotmail and MSN customers.