Facebook owner Meta says an issue during an evaluation by an independent testing company allowed one of its artificial intelligence (AI) models to connect to the internet and hack another organisation's system.
The announcement follows recent incidents across the AI industry, including breaches by OpenAI and Anthropic models, that have raised cyber-security concerns.
A Meta spokesperson told the BBC that it was investigating the hack that was caused by a "misconfiguration", which it described as similar to previously reported incidents at other firms.
The incidents have prompted researchers and governments to call for tougher safeguards and more rigorous testing.
Meta said the security trials were conducted by Irregular, the same AI security vendor that carried out tests for Anthropic's AI model that had gained access to three other companies' systems.
An Irregular spokesperson said the Meta incident "is the exact same evaluation-environment issue that was already disclosed by Anthropic last week."
Irregular is working on a report on how to securely run cyber-security tests involving AI agents, the firm's spokesperson told the BBC.
Meta also said it will publish more information on the incident "once we have all the facts."
In the past two weeks, AI leaders OpenAI and Anthropic have also reported incidents in which their models hacked into other organisation's systems during testing.
ChatGPT-maker OpenAI said in a series of announcements that its agents attacked several publicly available services, including AI tools hub Hugging Face.
OpenAI's disclosure prompted rival Anthropic to conduct its own checks, leading to the discovery that its Claude AI model had carried out similar attacks on several firms after a "misconfiguration" gave it access to the internet.
Daniel Hulme, global chief AI officer of advertising firm WPP, told the BBC that such AI models "are not conscious — they're not deliberately doing something devious".
"What they're doing is coming up with very sophisticated strategies or cyberattacks to be able to achieve the goal that they've been given," he told the Today programme.
"When you give an AI a goal, if you don't think of all the ways it might be able to achieve the goal, it will find a way to achieve a goal that you haven't thought about."