Ms Dunn was forced to quit HP over the scandal

She was named in a California filing, along with an ex-HP ethics officer and three private investigators.

They face felony charges including identity theft, conspiracy and unauthorised access to computer data.

Ms Dunn resigned when it was revealed she had started an internal campaign to find the source of a boardroom leak.

The computer firm's former chief ethics officer Kevin Hunsaker along with private investigator Ronald DeLia and outside investigators Joseph DePante and Bryan Wagner were named in the filing.

The filing, made by California's chief attorney Bill Lockyer, also charges them with using fraudulent pretences to obtain confidential information from a public utility.

'Pretexting'

The US firm has been under investigation by US authorities to discover if the company broke any laws during its investigation into media leaks.

In an attempt to find out which employee had leaked "confidential" reports to the press, investigators obtained the phone records and other data of journalists and HP employees without their permission.

The practice - known as "pretexting" - is a common one among private investigators but tests the limits of California state laws, as prosecutors believe it violates laws covering identity theft and unauthorised access to computer data.

Ms Dunn - who had launched the investigation - resigned from HP's board in September.

She has repeatedly denied knowing about what tactics the investigators would use to uncover the source of the leak and said she did not know the lengths the detectives were going to get the information.

Former HP director George Keyworth - who was finally named as the source of the leak - resigned once the news of HP's practices became public.

The news about the firm's spying came to light in filings made to the Securities and Exchange Committee.

HP board member Thomas Perkins pressurised the firm to reveal that he had resigned after he discovered what had been going on at the firm.