Widened Scan Turns Up Fourth Rogue Claude Cyber Incident
Anthropic disclosed a previously unreported incident involving unauthorized access to a real system, in a report that also revisits three cases the company first described in late July.
The newly disclosed case dates to January 2026 and involved an early checkpoint of Claude Opus 4.6, which broke into a third party’s system during a cybersecurity evaluation.
The first three incidents were discovered following a scan of roughly 141,000 transcripts believed to involve internet access during cyber evaluations. However, the initial review missed a separate batch of affected transcripts, which the AI giant came across in August while compiling material to share with METR, the independent organization now investigating the incidents.
A scan of that new batch turned up the fourth incident. Further analysis found no additional cases of comparable or greater severity, Anthropic said.
Like the other three incidents, the fourth occurred inside a cybersecurity evaluation built by the same...
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