Last week's News story on counter-terrorist technology (see Nature 413, 238; 2001) incorrectly described PerkinElmer Instruments' Threat Image Projection system as a software package that relies on pattern-recognition algorithms to spot weapons and other suspicious objects during X-ray baggage screening. In fact, the system is designed to monitor and improve the watchfulness of airport staff by randomly projecting images of such objects onto X-ray images of screened baggage.