Meta’s decision to introduce end-to-end encryption for Facebook messages will hamstring the rescue of child sex trafficking victims and the prosecution of predators, according to child safety organizations and US prosecutors.

This week, the tech giant announced it had begun rolling out automatic encryption for direct messages on its Facebook and Messenger platforms to more than 1 billion users. Under the changes, Meta will no longer have access to the contents of the messages that users send or receive unless one participant reports a message to the company. As a result, messages will not be subject to content moderation unless reported, which social media companies undertake to detect and report abusive and criminal activity. Encryption hides the contents of a message from anyone but the sender and the intended recipient by converting text and images into unreadable cyphers that are unscrambled on receipt.

Social media companies are legally obligated to send any evidence of child sexual abuse material they detect to the National Center for Missing & Exploited Children (NCMEC) in the US, which then forwards it to relevant domestic and international law enforcement agencies.

“Encryption on platforms without the ability to detect known child sexual abuse material and create actionable reports will immediately cripple online child protection as we know it,” said an NCMEC spokesperson. “NCMEC anticipates the number of reports of suspected child sexual abuse from the larger reporting companies will plummet by close to 80%.”

Meta, the parent company of Facebook, Instagram and WhatsApp, submitted nearly 95% of the 29m reports NCMEC’s CyberTipline received from tech companies in 2022. A large proportion of these tips depicted child sexual abuse material in which children are being raped, abused and sexually exploited, according to the organization.

The identification and rescue of exploited children would be made more difficult by encryption, as investigators would often only be able to identify victims by gaining access to a suspect’s social media accounts and private messages, said Ali Burns, an assistant US attorney in Illinois.

“To get the messages, it’s going to rely on us finding their physical phones. But as far as getting a tip if something happens, if those aren’t being monitored, it will definitely change the cases and what we’re currently made aware of,” Burns said. Burns has prosecuted cases of predators using Facebook and Messenger to groom teenagers. “It would make it more challenging to corroborate evidence, to be able to verify. I can see this being a challenge for law enforcement.”

Civil rights groups argue, however, that end-to-end encryption protects individuals’ personal data and free expression. Creating a loophole in user protections for one use case inevitably leads governments and other bad actors to use those entry points for surveillance and other nefarious purposes, they argue.

“This level of security not only protects individuals from cyber-attacks but also empowers citizens to communicate freely without fear of surveillance, censorship, and warrantless searches – whether by the government, Big Tech, data brokers, or anyone else,” read an October statement from the American Civil Liberties Union, a non-profit human rights organization.

Meta said in a statement to NBC: “We don’t think people want us reading their private messages so we have spent the last five years developing robust safety measures to prevent and combat abuse while maintaining online security. We continue to strengthen our enforcement systems to root out potentially predatory accounts.”

Messenger is no stranger to content depicting the abuse of children. A Guardian investigation in April revealed how Meta is failing to report or detect the use of its platforms for child trafficking and uncovered how Messenger is being used as a platform for traffickers to communicate to buy and sell children. In 2018, a video of an adult man sexually abusing an underage girl spread to thousands of people via Messenger under the guise of outrage over what the video showed.

Encryption will create barriers to collecting evidence and prosecuting criminals who want to target children over Meta platforms, child sex trafficking experts said.

“It is a dereliction of their ethical and moral duty of care to society to knowingly bring about changes to their platform, knowing full well that the net effect will be to mask and provide plausible deniability over a problem they have failed to contain over the years,” said Lianna McDonald, executive director of the Canadian Centre for Child Protection, a non-profit. “Regulation cannot come soon enough.”

Kristina Korobov, senior attorney for the non-profit Zero Abuse Project and former assistant US attorney in Indiana, called encryption “a real threat to kids”. She said the dangers of Facebook hide behind a veil: “It’s often viewed as ‘safe’ by parents for use by teens.”

In one of Burns’s recent cases in Illinois, an American man named Joseph Fuchs was sentenced to 126 months of jail in December 2022 for grooming a 14-year-old child in the Philippines and traveling there to engage in illicit sex with her.

Fuchs, 52, had located the girl on Facebook and groomed her over Facebook Messenger. Illinois law enforcement was alerted to Fuchs’s crimes by a report that Meta made to NCMEC. Transcripts from Fuchs’s trial show some of the communications between Fuchs and the child took place over Facebook Messenger, which investigators say they were able to obtain because the communications were not encrypted.

“In this case, we wouldn’t have ever known about it if Facebook had not flagged it,” said Burns.

• In the US, call or text the Childhelp abuse hotline on 800-422-4453 or visit their website for more resources and to report child abuse or DM for help. For adult survivors of child abuse, help is available at ascasupport.org. In the UK, the NSPCC offers support to children on 0800 1111, and adults concerned about a child on 0808 800 5000. The National Association for People Abused in Childhood (Napac) offers support for adult survivors on 0808 801 0331. In Australia, children, young adults, parents and teachers can contact the Kids Helpline on 1800 55 1800, or Bravehearts on 1800 272 831, and adult survivors can contact Blue Knot Foundation on 1300 657 380. Other sources of help can be found at Child Helplines International