Facebook is heing hit with a class action lawsuit over claims of monitoring its users’ private messages without their consent in order to mine information for its own profit.

Being issued on behalf of about 166 million Facebook users in the US, the lawsuit filed by plaintiffs, Matthew Campbell and Michael Hurley, accuse the social networking site of sharing the mined data with marketers, data aggregators and advertisers.

Claiming the allegations as ‘without merit’, the social networking major said: "We will defend ourselves vigorously."

The lawsuit filed with the US district court for Northern California said: "Representing to users that the content of Facebook messages is "private" creates an especially profitable opportunity for Facebook, because users who believe they are communicating on a service freefrom surveillance are likely to reveal facts about themselves that they would not reveal had they known the content was being monitored."

Citing independent research, the lawsuit claimed that when a user shares a link to another site in a personal message, Facebook records it to contribute to a profile of the sender’s web activity.

The latest suit looks to claim either more than $100 a day for each day of alleged violation, or $10,000, for each user alleged to be influenced.

This is not the first time the social networking site has been hit with a lawsuit over its privacy policies. It was previously criticised over proposed modification to its privacy policy, which aimed to enable the development of ads using the names and profile pictures of its users.