A top official in a key Montgomery County development agency tried to block an internal investigation of failures in the agency’s computer security system, The Examiner has learned.

Montgomery County Planning Director Rollin Stanley told his staff that a review of his agency’s Internet firewall failures was “a fishing expedition” and intervened to keep investigators from interviewing his staff, internal documents reviewed by The Examiner show. The agency’s firewall had problems nearly 300 times — an average of 24 times per month — in a little more than a year between 2008 and 2009.