Ms Dunn was forced to quit HP over the scandal

Ms Dunn is due to appear before the US House Energy and Commerce Committee's investigative subcommittee later.

In a prepared statement she is expected to name HP's finance director as the person who instigated the inquiry.

US authorities have been investigating whether HP broke any laws during its investigation into media leaks.

In an attempt to discover 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.

Legality 'assumed'

Ms Dunn has consistently denied knowing about what tactics the investigators would use to uncover the source of the leak.

In her prepared statement for the House Committee, she says she was under the impression that finance chief Bob Wayman had given the go-ahead for the investigation.

"It was my assumption that Mr Wayman, having ultimate authority over all the resources involved in security and investigations, as well as having been one of the directors who felt the most strongly about the importance of controlling leaks from the board, had provided authorisation for whatever work was undertaken," Ms Dunn's statement says.

The written testimony also adds that she asked private investigator Ron DeLia if his methods were legal and complied with HP's "normal practices".

"I never doubted... that what they were doing was legal," her statement, released by the committee's hearing panel, adds.