Steven Spielberg is said to be so paranoid about security he has a getaway motorbike permanently parked outside his office.

A new book, written by journalist Nicole LaPorte, alleges the 'Indiana Jones' director keeps the never-before-used bike for the gravest emergencies and at one point his employees were issued with 'survival kits' which included gas masks.

LaPorte also claims he is so secretive he verges on "near-paranoia" and abides by several bizarre practices to keep his business secret, including keeping a "dome of silence" above his desk.

One extract from 'The Men Who Would Be King: An Almost Epic Tale of Moguls, Movies, and a Company Called DreamWorks' reads: "In Spielberg's office, hanging above his desk, a plexiglass half-moon keeps sound from reverberating so that his phone conversations remain ultra-confidential. When an assistant once asked what the funny thing over Spielberg's desk was, a security guard referred to it as a 'dome of silence'."

Another extract alleges: "When Spielberg's long-time editor views footage in the screening room, a black cloth is draped over the projection booth window to hide the screen."

While a third extract claims: "Every document that leaves the office - a script, development report, even a memo - is coded, so that should it somehow get into the wrong hands, the person responsible for the breach can be identified."

Spielberg's representative has denied the claims in the book and insists they are not true.

The spokesperson said: "This description is so far from the real world of Steven that it doesn't deserve a comment.

"If the rest of the book is like this excerpt, readers can expect very little of what they read to be true."

LaPorte has defended her work, however, saying although none of the DreamWorks founders would talk to her, she has spoken to nearly 200 current and former employees.