British workers are not good at keeping their computer passwords secret, with two-thirds ready to reveal them to a stranger in exchange for a chocolate bar and a smile, a study has found.

The report, by Infosecurity Europe, the organisers of the annual IT security trade show, involved stopping commuters at London's train and underground stations and asking them to take part in a survey in exchange for a chocolate bar.

Researchers asked commuters if they knew what the most common password was and then asked them to reveal their own. About 40 per cent of commuters revealed their computer password straight away, with a further 22 per cent giving up details with a little further probing from the female researchers.

The same study was also done at an exhibition for IT professionals, with similar results. Only 22 per cent of IT workers revealed passwords quickly but 42 per cent yielded details under further questioning.

The study demonstrates how vulnerable passwords are to simple social engineering techniques that can be used by criminals.