A jury in New Mexico sided with the state attorney-general’s office in a landmark United States case accusing social media giant Meta of allowing its social media platforms to become venues for child predators to solicit young users.

The jury ordered Meta to pay $375 million ($642m) for violations of the US state’s consumer protection laws in its verdict, delivered today.

“The jury’s verdict is a historic victory for every child and family who has paid the price for Meta’s choice to put profits over kids’ safety,” New Mexico Attorney-General Raul Torrez, a Democrat, said in a statement.

“Meta executives knew their products harmed children, disregarded warnings from their own employees, and lied to the public about what they knew,” he added.

“Today the jury joined families, educators, and child safety experts in saying enough is enough.”

Investigators from the New Mexico Department of Justice went undercover on Facebook in an effort to gather evidence on the effects of the site’s algorithms and alleged lack of protections for young users.

Over a multi-week trial in Santa Fe, they presented allegations that Meta broke state laws, arguing that young Meta users were at risk of being exposed to sexual abuse images or messages from would-be predators.

“Meta’s platforms Facebook and Instagram are a breeding ground for predators,” the state alleged in a court filing.

The state’s probe also resulted in criminal charges against three men.

They included one who had previously been banned from Facebook for being a convicted sex offender, but who authorities alleged returned to the site and began an inappropriate chat with an 11-year-old girl before being caught in a sting operation.

Meta said immediately after the verdict that it would appeal.

“We work hard to keep people safe on our platforms and are clear about the challenges of identifying and removing bad actors or harmful content,” Meta spokesman Chris Sgro said in an email.

“We will continue to defend ourselves vigorously, and we remain confident in our record of protecting teens online.”

The verdict is a rare US courtroom victory for plaintiffs trying to hold the tech industry accountable for activity on online platforms in the face of broad legal protections it has enjoyed since the 1990s.

Mary Graw Leary, a law professor at Catholic University, said the result is significant because it shows that those shields are not impenetrable.

“When companies operate in that kind of a world, they choose profit over children and safety because they have no incentive to do otherwise,” Graw Leary said in an email.

“This verdict signals that tech can be held accountable for these business decisions, which may change their incentives.”

Meta and other companies are now facing several cases alleging that their platforms are harmful to children and teens.

The cases have worked around the companies’ legal protections by focusing on product design choices.

The New Mexico verdict comes as a separate jury in Los Angeles, California, is weighing a case in which a young social media user alleged that she had become addicted to Instagram and YouTube.

A separate trial in the New Mexico case is scheduled for May, when the state will try to persuade a judge to impose further financial penalties and order changes to the design of Meta’s platforms to improve child safety.

Torrez wrote to Meta chief executive Mark Zuckerberg in December, asking for changes including age verification, reduction of risks created by encrypted chat features, changes to algorithms and the removal of “bad actors”.

While the trial was underway, Meta said it would end fully encrypted chats on Instagram, shutting down a privacy feature that law enforcement has argued makes it harder to uncover wrongdoing.