Hurd told a news conference Dunn's resignation was effective immediately and that he would take over her duties as chair of the HP board.

"We believe it is in the company's best interest that she now step aside given the distraction her presence on our board continues to create," Hurd said. "We have never questioned her intentions, her integrity or her ethics."

Dunn had been due to step down in January 2007 but her departure was moved up amid allegations HP's investigators impersonated board members and journalists to get private telephone records.

"Some of the findings uncovered are very disturbing to me," Hurd said at the company's office in Palo Alto, California.

"On behalf of HP I extend my sincere apologies to those journalists investigated and everyone who was impacted."

Hurd said that his offer to testify with Dunn and HP lawyers before the House of Representatives' Energy and Commerce Committee in Washington on September 28 had been accepted.

The hearing will focus on whether private investigators hired by HP spied on board members, employees and reporters in a campaign to plug a company leak.

At issue was whether the investigators impersonated people to gain access to their telephone records, secretly followed people, and tried to trace company e-mail to learn where it was forwarded.