By Ana-Maria Stanciuc
Publication Date: 2026-11-11 08:30:00
Some neurons in large language models are rarely activated. Microsoft researchers have found a way to turn fewer than 10 of these dormant neurons into a hidden backdoor, making an otherwise normal AI model behave as expected until it encounters a specific trigger. Once activated, the model can execute malicious commands.
The technique, called Lazarus, is described in a Microsoft Research post by principal researcher Dimitris Papailiopoulos. It does not require retraining the model.
Instead, the researchers found that pretraining creates such a structured internal representation that a simple classifier, trained on roughly 50 examples, can distinguish triggered inputs from ordinary ones. A dormant neuron can then be reprogrammed to recognise the trigger.
When that happens, the neuron forces a chosen token into the model’s output. By linking several modified neurons, an attacker can generate longer sequences of instructions that execute in a terminal.
The…
