# Lazarus

Microsoft researchers describe Lazarus, a backdoor that needs no retraining: rewriting fewer than 10 rarely firing dormant neurons in a large language model is enough to make an AI agent built on it execute attacker commands when a hidden trigger appears. The trigger can be as mundane as a date change, the model passes standard evaluations, and reliable detection requires diffing weights against the original, so provenance and weight integrity become central.

Microsoft researchers describe Lazarus, a backdoor that needs no retraining: rewriting fewer than 10 rarely firing dormant neurons in a large language model is enough to make an AI agent built on it execute attacker commands when a hidden trigger appears. The trigger can be as mundane as a date change, the model passes standard evaluations, and reliable detection requires diffing weights against the original, so provenance and weight integrity become central.