A method and apparatus for operating a portable computer configured for docking to a docking station is disclosed. In one embodiment, a portable computer system includes a docking interface having a bus switch and a bus monitoring circuit, and a bus coupled to the docking interface. With the computer coupled to a docking station, the bus switch, when closed, may couple the bus to a peripheral interface in the docking station. The bus switch may close responsive to docking, thereby completing the electrical coupling of the bus to the peripheral interface in the docking station. The portable computer being docked to the docking station, the bus monitoring circuit may monitor the bus cycles occurring on the bus and identify trusted read and/or write cycles. During trusted bus cycles the monitoring circuit may operate to open the bus switch thereby preventing information transmitted during the trusted cycles to be accessible outside of the portable computer system, even with the portable computer system remaining docked to the docking station. The monitoring circuit may also operate to close the bus switch in response to a currently occurring trusted bus cycle being interrupted, aborted and/or completed.