Behavioural signal collapses against a competent replay: a measurement
With real human data, mouse dynamics separate a person from a simple script almost perfectly and drop to a third of the hit rate against a smooth replay of the human movement itself; keyboard dynamics fall to chance. Passive observation cannot tell a competent copy from the original, so a passive signal serves to decide when to challenge, never as proof of presence.
Method: Three public sets of human data (free mouse, fixed-text keyboard and free-text keyboard) against scripts at four levels of sophistication, plus a smooth replay of real human traces, validated by a gate that checks whether it preserves the microstructure of the movement. Metric at the operating point: human hit rate at a false alarm rate of at most 1%, evaluated per session and across people, with the worst person as the indicator. No keystroke content captured; no pooling of sets into a single class.
Source: Hummand measurement bench (private repository). Human data: Balabit Mouse Dynamics Challenge (mouse), Killourhy and Maxion, CMU (keyboard, fixed text), and Dhakal et al., Aalto 136M (keyboard, free text). Measured on 2026-06-27.
Read the note