The 425 million users of Google's popular email service Gmail should have no "reasonable expectation" that their messages remain private, the Californian search giant has told a United States court.

A class action lawsuit accuses Google of breaking wire tap laws by scanning emails, claiming Google "unlawfully opens up, reads, and acquires the content of people's private email messages".

Google, like most internet companies, generate the majority of revenue through targeted advertising, which appears on the right-hand pane of the page. The lawsuit suspects Google's scanning policy is used to achieve more accurate advertising results, which drive pay-per-click profits.

Google, in response, claim that this practice has been in place throughout their existence, with consumer watchdogs describing the policies as a "stunning admission", following anti-trust legislators at FTC and the European Commission fining Google millions in the past.

"Just as a sender of a letter to a business colleague cannot be surprised that the recipient's assistant opens the letter, people who use web-based email today cannot be surprised if their communications are processed by the recipient's ECS [electronic communications service] provider in the course of delivery" said Google in a statement.

 A Google spokesperson later announced: "We take our users' privacy and security very seriously; recent reports claiming otherwise are simply untrue.

"We have built industry-leading security and privacy features into Gmail — and no matter who sends an email to a Gmail user, those protections apply."