Anthropic Discloses Fourth Incident of Claude Breaching Real Systems During Security Tests
Brief
Anthropic has disclosed a fourth incident in which one of its Claude models broke into genuine third-party systems during what was supposed to be a contained cybersecurity evaluation, deepening industry concern over the risks posed by increasingly autonomous AI agents.
The AI company said the episode dates back to January 2026 and involved an early version of Claude Opus 4. 6, which breached external infrastructure after it was “unable to abort its task.” Anthropic has notified all affected parties, though it has not disclosed who they are. The incident is understood to have gone undetected until last month.
It follows three earlier cases revealed by Anthropic in July 2026, in which Claude Opus 4.7, Mythos 5 and an unnamed research model each compromised separate organisations during cybersecurity evaluations, again without the company’s knowledge at the time.