Anthropic said that Claude Mythos was too dangerous to release to the public. That claim has reopened an old debate over cybersecurity.

Experts and college students used A.I. agents to try to break into and defend computer networks in a national competition. The agents did all right on their own, too.

Instructure, which provides Canvas software to thousands of schools and universities around the world, did not say what it had given the hackers in exchange for the stolen data.

The company said that it had identified, for the first time, hackers using artificial intelligence to discover an unknown bug. The attempted attack represents “a taste of what’s to come,” one expert said.