When my daughters were first introduced to the TV thriller series 24, they would be fizzing at the end of each cliff-hanging episode, pulses racing and minds buzzing. It was the same adrenalin-fuelled state computer gamers can slip into after a violent virtual-world encounter.

It is frightening how people can be so affected by what they see on a screen; and as interfaces and graphics become more realistic and online worlds more inventive, so they become more absorbing and potentially dangerous.