Hewlett Packard's CEO, Mark Hurd, has apologised for "instances of impropriety" over how his company conducted an investigation of boardroom leaks, at the same time as he announced the immediate removal of chairman Patricia Dunn.

Faced with a deepening scandal over the possibly criminal methods used by the investigation, Hurd explained his role in it and said he first learned of the effort in July 2005. "This is a complicated situation and the more I look into it, the more complicated it becomes," he said at a press conference late on Friday at the company's California headquarters. "As of today, we still do not have all of the facts."

Dunn had already announced plans to step down as chairman in January over the scandal and intended to stay on the Board after that, but Hurd announced she had now left the company entirely. Hurd himself has replaced her as chairman, breaking HP's own corporate governance guidelines that say that one person should not serve as both CEO and chairman - guidelines that have been rewritten and reposted on HP's website just prior to the announcement.

Hurd refused to take questions, but a spokesman promised company officials would answer before a US House sub-committee investigating the scandal later this week.

HP worked with private investigators who obtained telephone records of board members, reporters and possibly others through a practice known as "pretexting" - pretending to be someone else. Civil as well criminal charges are possible, California attorney general has warned.

"What began as an investigation with the best intentions has ended up turning in a direction we could not have possibly anticipated," Hurd said. "The people of HP don't deserve this nor do any of the people who were impacted. On behalf of HP, I extend my sincere apologies to those journalists who were investigated and everyone who was impacted."

Computerworld's Angela Gunn, Todd R. Weiss and Ken Mingis contributed to this report.