Hoffman, the company's top executive since January 2003, will continue in the role during a transition period, Ninemsn said in a statement today.
"Ongoing developments in the media and technology industries mean now is the right time to seek new opportunities to use my strengths of hands-on leadership in building businesses," said Hoffman in the statement.
The Australian bosses of both PBL and Microsoft said Hoffman was welcome to choose a role at either company.