Yahoo! has been accused of changing its terms and conditions to allow it to read its customers' private emails.
The world's biggest email provider says that by signing up to its service, users are giving their consent for both their outgoing and incoming mail to be analysed for information to sell targeted advertising.
The responsibility for telling non-Yahoo! customers that their emails and messaging content are being read is placed on the user.
'Most consumers would be horrified to learn that their email can be read in order to open the door to targeted advertisers.'