By Jonathan Davies

Internet giant Yahoo will face legal action in the US for allegedly spying on the content of emails sent to its own users from non-Yahoo accounts.

A judge in California ruled that those who have sent emails to, or received emails from, a Yahoo account since 2 October 2011 can sue Yahoo as part of a group. Reports suggest that there are roughly one million people who take action.

Yahoo has 275 million email users, and the class action lawsuit accuses it of accessing the content of emails to create "targeted advertising" for its users.

Around 80% of Yahoo's revenue comes from advertising.

Yahoo has defended itself, claiming that non-Yahoo email users continued to email Yahoo accounts despite being aware of the activity, and therefore consented to Yahoo's actions.