01/03/2014 12:33 EST | Updated 01/25/2014 04:01 EST

Facebook Lawsuit Alleges Site 'Reading Its Users' Personal Messages'

ARCHIV: Das Logo des Online-Netzwerkes Facebook in Muenchen ist durch eine Lupe auf dem Computer-Bildschirm eines Laptops fuer eine Fotoillustration zu sehen (Foto vom 11.10.10). Facebook veroeffentlicht am Mittwoch (31.01.13) das Ergebnis fuer das vierte Quartal 2012. Foto: Joerg Koch/dapd

A class-action lawsuit filed against Facebook says the social network “systematically violated consumers’ privacy by reading its users’ personal, private Facebook messages without their consent.”

The lawsuit, filed in a U.S. District Court in California on Dec. 30, says Facebook scans private messages for external links embedded in them, then opens the those links to scan the page. If the page contains a Facebook “like” button, it counts the link in the private message as a “like” for that page, the lawsuit says.

The filing says Facebook is violating the U.S.’s Electronic Communications Privacy Act, and is seeking “the greater of $100 a day for each day of violation, or $10,000” for every person who joins the class-action lawsuit. It also wants the court to bar Facebook from further interception of private messages.

The lawsuit suggests Facebook is misleading users by making them think private messages are not shared with outside parties.

This “creates an especially profitable opportunity for Facebook, because users who believe they are communicating on a service free from surveillance are likely to reveal facts about themselves that they would not reveal had they known the content was being monitored,” the suit states.

Facebook told CNET News the allegations “are without merit” and the company plans to defend itself “vigorously.”

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Much of the lawsuit is based on research carried out earlier this year by Swiss security firm High-Tech Bridge, which created unique URLs not known to the public that it added to messages on social networks, creating “traps” to see who would click. Facebook was one of the sites where the URLs were clicked. Google+ and Twitter also appeared to be doing something similar in those tests.

Other websites are also facing legal action for allegedly intercepting private communications.

Google is currently facing a lawsuit over its Gmail service, which scans the content of emails to serve up customized ads to users. The practice amounts to a violation of U.S. wiretapping laws, according to a lawsuit filed in a U.S. District Court in September, 2013.

Google has criticized the lawsuit as an attempt to "criminalize ordinary business practices" that have been in place for nearly a decade.