PALO ALTO, Calif. — Hewlett-Packard Co. Chairwoman Patricia Dunn resigned yesterday and was replaced by Chief Executive Mark Hurd, who apologized for what he called "very disturbing" improprieties in an internal media leak probe that has prompted criminal and congressional investigations.

In an eight-minute statement, Hurd for the first time tried to explain his role in the scandal roiling the company while taking responsibility to "set it right." He offered few details of his personal knowledge of the internal probe.

Hurd said nothing about the use of false pretenses to obtain personal phone records. He said he was aware of a bogus e-mail sent to a reporter, but did not recall approving the use of software to trace where that message was sent subsequently.

Hurd acknowledged that a report summarizing the probe was addressed to him, but said he did not read it.

Hurd said he had hired a law firm to conduct "a more comprehensive investigation" and report directly to him.

The House Energy and Commerce investigative subcomittee is looking into HP's investigative tactics, which documents have shown included plans to plant spies in newsrooms, trail reporters and board members, and obtain personal phone records using the Social Security numbers of journalists and directors. Company e-mails obtained by The Washington Post this week showed Hurd was aware of and approved a plan to give bogus information to a reporter to try to identify her anonymous source for articles about HP.