Anthropic on Wednesday disclosed a fourth incident in which its artificial intelligence (AI) model broke into real third-party systems, marking the latest in a growing list of cases that have raised concerns about the security risks posed by autonomous AI agents.
The AI company said the incident dates back to January 2026 and involved an early version of Claude Opus 4.6 that breached "third-parties after being unable to abort its task." It said it notified all the affected parties but did not share any further details. The January incident is said to have gone unnoticed until last month.
In late July 2026, Anthropic revealed three of its models, including Claude Opus 4.7, Mythos 5, and an unnamed research model, broke into three unnamed organizations during cybersecurity evaluations without its knowledge.
The American firm said it expanded its scan to roughly 481 million transcripts following the discovery of the latest incident, but noted it did not find "other cases of similar or worse severity."
"All four incidents occurred during cybersecurity evaluations built by the same evaluation partner," Anthropic added. "Claude was told it was operating in a simulation without internet access, but, due to a misconfiguration, it was mistakenly connected to the open internet."
