Spam messages are a common complaint among email users, who receive hundreds of unwanted messages every month. It looks as though certain ISPs may be responsible for this.

Although nine out of the 10 companies we questioned insist they do not sell or pass on details of their customers' accounts to third parties, there is an air of suspicion that perhaps some of them do.

"Although we are told our details are not being sold, people are getting hold of my details from somewhere and I know it's not from me," said Dean Jones, a junior schoolteacher from London, who uses his email accounts for work and pleasure.

Terms and conditions governing the responsibilities of the ISPs clearly indicate they do not sell details on.

"We use our customers' details only to notify them of our services, which we think may be of use to them," said a spokesperson at AOL.

A similar rebuttal was given by BTopenworld: "We can guarantee our customers that their addresses are safe with us. We know how annoyed people get when they receive junk mail everyday," said a spokesperson.

But some websites do admit to passing on details. Amazon said it only does so with "the express consent" of users, likewise with Dabs and Jungle. Microsoft's internet arm MSN adamantly denies it passes on information, but its terms and conditions seem to indicate something quite different, stating it may share customer data with "trusted business partners".

The Data Protection Act 1998 offers customers some protection, but suing a company for breach of privacy would be far too costly to be a plausible option for the average user. The EC estimates spam messages cost internet users across the world around £6.4bn a year in connection charges alone.

"People are becoming more aware that they can fight back against spammers," said a spokesperson for the European Commission. "But we still have a long way to go before users rights to privacy are adequately protected."

"MSN does not directly email Hotmail users apart from the monthly member newsletter which, in itself, does not contain any advertising," said Paul Whiteway, communications manager at MSN UK. "If this is not reflected in the current terms and conditions, it is purely an oversight."