In a motion to dismiss a class action lawsuit against them, Google admitted its 400 million Gmail users should not expect privacy in their email correspondence, Business Insider reported.

The court briefing, obtained by Consumer Watchdog, stated anyone sending information with a third party should know the contents would be subject to a breech in privacy.

"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 provider in the course of delivery," Google's lawyers said in the filing. "Indeed, a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties."

The filing also pointed to the 1979 case of Smith vs. Maryland. In that case, a telephone call was routed through the company's systems and was therefore accepted that the call's communications should be subject to observation.

When someone "voluntarily convey[s] numerical information to the telephone company and 'expose[s]' that information to its equipment in the ordinary course of business,"
 Google's filing read.

U.S. Supreme Court Justice Sonia Sotomayor cited the same case in Jan. 2012, but argued a business transaction over the phone or Internet should not automatically be deprived of the rights under the Fourth Amendment.

"Google has finally admitted they don't respect privacy," said John M. Simpson, Consumer Watchdog's Privacy Project director, in a news release. "People should take them at their word; if you care about your email correspondents' privacy don't use Gmail."

While Google claims to use email content for spam filters, targeted advertising and other Gmail services, opposition to the motion to dismiss said the Internet giant has its own "secret use" for such information.

"If you have something that you don't want anyone to know, maybe you shouldn't be doing it in the first place," Google CEO Eric Schmidt told CNBC in 2009. "But if you really need that kind of privacy, the reality is that search engines, including Google, do retain this information for some time. And ... we're all subject, in the United States, to the Patriot Act, and it is possible that that information could be made available to the authorities."