Asmall doorway in the hillside, in the middle of a hay meadow in Wiltshire, is the only outward sign of Symantec's internet security operations centre.

The facility is buried underground, under a metre and a half of concrete, in a former Ministry of Defence nuclear bunker. The walls are 46cm thick and the site is entered via an airlock consisting of four steel doors the thickness of sprung mattresses. There are no windows to the outside world and the bunker has its own power generator and air-filtration system, which would allow it to survive, sealed off, for 40 days after a nuclear attack.