From my understanding and IANAL there are two main problems.

1) most law requires intent, especially criminal. OpenAI certainly didn't "intend" to hack these companies given they did sandbox them etc.

2) Given the agent hacked them, not a human, a lot of law requires a person/employee to have done it to hold the company liable if it was part of their work duties.

I think the only real potential ground is negligence (in not sandboxing them correctly and being reckless with running these tests at all), but this requires not taking reasonable precautions. They could argue that they _did_ but it was so novel the precautions failed. But it's important to say if this happens again in the future it's arguably much harder to try and make this case.

Interestingly this was solved with new laws for self driving cars, most of which assign the company that is operating the car as the "person" involved explicitly.