When it infects the lungs, the Legionnaire’s bacterium Legionella pneumophila causes acute pneumonia. The pathogen’s modus operandi is particularly ingenious: it infiltrates deliberately into cells of the human immune system and injects a host of proteins which then interfere in the normal cellular processes. Scientists have now discovered how Legionella reprogrammes the cells to ensure its own survival and to propagate. They examined a protein used by the pathogen to divert the material transport within the cells for its own purposes.