A hacker broke into more than 100 websites using an army of AI agents that mostly operated on their own, according to findings from the AI security firm Norforge. Though Norforge doesn’t name the targets, Reuters reports that the victims included companies like John Deere, SharkNinja, and Cummins.

Researchers at Norforge uncovered the attacks through exposed work on Cairn, an open-source AI platform that describes itself as a “general-purpose problem-solving engine.” With Cairn, users set a start and end point for the AI agents, which document their progress as they move forward with the task. However, as noted by Norforge, hackers can also use the tool to orchestrate cyberattacks using AI agents.

The hacker who broke into more than 100 sites was the “most active” among the exposed Cairn instances discovered by Norforge, waging attacks on companies based in the US, Canada, Australia, and Japan, as reported by Reuters. This attacker laid out “preferred intrusion tactics” using fewer than 100 Chinese characters, with successful breaches taking about 23 hours, according to Reuters. Overall, Nordforge found more than 20 exposed Cairn instances that are “likely malicious.”

In a statement to Reuters, a John Deere spokesperson said there is “no indication that ​sensitive information was accessed” as a result of the attack, while Cummins said it’s “investigating the report of a potential cyber-attack on a website operated by one of our third-party vendors.”

Meanwhile, SharkNinja says the breach impacted a standalone site with product support information, and that it has contained the threat. John Deere, Cumms, and SharkNinja didn’t immediately respond to The Verge’s request for comment.

Nordforge says it’s working to get the malicious Cairn instances taken down. Cairn’s creator, who goes by @le1xia0, said earlier this month that the platform “was never a ‘hacking tool,’” adding that “misuse is a human decision, not a feature of the engine.”