Internet giant Yahoo has been condemned over plans to snoop on emails in a 'blatant intrusion of privacy'.

The US company provides an email service for thousands of Britons, including children, who will assume that the system is completely private.

However, it has emerged that Yahoo has changed its small print terms and conditions to get permission to view and scan emails.

Blatant intrusion: Yahoo has been condemned for plans to snoop on emails for advertisers

At the same time, the firm will also be able to spy on incoming emails from individuals and businesses without permission or warning.

Yahoo is pressing ahead with the change on the basis it will allow the company to identify which celebrities, subjects, sports, hobbies and products a particularly customer is interested in.

In future, it would use the information to target the customer with website advertising and product information that is relevant to these areas.

The Yahoo customer visiting a range of websites would then see pop-up advertisements that are relevant to keywords in outgoing and incoming emails.

Yahoo is among a number of internet companies and email service providers who are able to scan customers emails for key words and phrases.

Big Brother Watch director Daniel Hamilton called on Yahoo to think again

The sifting of emails is done using computers, rather than individuals, and creates anonymous profiles of the likes and interests of customers which can be used for internet marketing.

The proposal was highlighted by Which? Computing magazine, whose editor, Sarah Kidner, said: 'This is a blatant intrusion of privacy. People should have the right to send messages without Yahoo snooping through them.'

Daniel Hamilton, the director of Big Brother Watch, agreed and called on Yahoo to think again.

He said: 'It's extremely disappointing that Yahoo has opted to intrude on privacy in this way.

'Web users have a right not to see their personal messages trawled through in order to boost Yahoo's advertising revenue.

'Yahoo should abandon these changes before the crucial bond of trust between it and its users is damaged beyond repair.'

The company has suggested that it is up to customers to warn family, friends, businesses and others who send them email that these may be viewed by Yahoo's computers.

This was rejected by Which? in-house lawyer Georgina Nelson, who said: 'The obligation to notify those who email you that their message will be scanned is nonsensical and unrealistic. When exactly are you supposed to do this?'

Yahoo said customers will receive a pop-up asking them to agree to the new terms and conditions.

It said: 'Users who choose to accept the new terms will allow Yahoo's computer systems to identify words, links, people and subjects from their email, so that we can deliver exciting new product features.

'In time, we will also serve relevant ads.'

The company said customers can opt out of internet-based ads by going to http://info.yahoo.com/privacy/uk/yahoo/