Facebook chief executive Mark Zuckerberg confirmed that communications sent over the Facebook Messenger app are not as private as users may think, Bloomberg reports. He said Facebook scans some images and messages for security purposes.

“On Messenger, when you send a photo, our automated systems scan it using photo matching technology to detect known child exploitation imagery or when you send a link, we scan it for malware or viruses,” a Facebook spokesperson told Bloomberg. “Facebook designed these automated tools so we can rapidly stop abusive behavior on our platform.” The scanned data is not used for advertising, she said.

Zuckerberg told Vox that scanning Messenger is a necessary precaution. “It is clear that people [are] trying to use our tools in order to incite real harm,” he said, citing an example of agitators using Messenger to stir up religious violence in Myanmar. “Our systems detect that that’s going on … We stop those messages from going through.”

The concern about Facebook Messenger is part of a larger concern about privacy on the platform, especially after news that data firm Cambridge Analytica harvested information from millions of Facebook users to construct voter profiles to influence election outcomes. Facebook knew about the data breach, but failed to notify those whose information had been taken without their consent.

A spokesperson for Facebook said on Wednesday that Cambridge Analytica may have mined 87 million user profiles, according to The New York Times. Zuckerberg is expected to testify on Capitol Hill about the breach next week.
(Originally published on RollingStone)