In 2013, Facebook took 700,000 users and filled their feeds with either all positive or all negative posts, to learn the effects of emotionally-charged information.

Facebook is used to being under fire for invading users' privacy

FACEBOOK could be forced to pay users up to $US10,000 ($A12,300) each for violating their privacy if a new lawsuit is successful.

A judge in the US District Court ruled on Wednesday that a class-action suit against the social media giant can proceed.

According to the lawsuit, originally filed in December 2013, Facebook scanned the content of users’ private messages for advertising purposes, violating the Electronic Communications Privacy Act and California’s privacy and unfair competition laws.

Whenever users included links to third-party websites in messages, Facebook would follow the link and search for information to profile the sender’s browsing activity, it was alleged.

According to court documents, Facebook would also treat a link to a website within a private message as the user having ‘liked’ that page via the embedded social share button.

Facebook had attempted to dismiss the suit by claiming the “interceptions” were lawful because they occurred in the “ordinary course” of its business.

Judge Phyllis Hamilton slapped down that argument this week, arguing Facebook had “not offered a sufficient explanation of how the challenged practice falls within the ordinary course of its business”.

She also hit out at Facebook’s suggestion that “any activity that generates revenue for a company should be considered within the ‘ordinary course of its business’”.

“At the hearing, Facebook’s counsel suggested that, because the practice is in the service of making money, it must necessarily fall within the ordinary course of business,” she said.



“However ... An electronic communications service provider cannot simply adopt any revenue-generating practice and deem it ‘ordinary’ by its own subjective standard.”

While Facebook ceased the practice in 2012, the company says it still analyses messages to protect against viruses and spam.

Google has come under fire for a similar message-scanning system.

The Facebook class-action would cover any Facebook user in the US who sent or received a private message in the last two years that included a web link.

Facebook has been contacted for comment.

frank.chung@news.com.au