This paper introduces PSCAN; a port scanning-based network covert channel that violates non-discretionary system security policy that does not allow data transfer from a given process (the sender) to another given process (the receiver). Using PSCAN, the sender opens and closes network ports in a way that encodes covert data. The receiver performs a synchronized port scanning procedure on the sender's host to determine which ports are open and which ones are closed then decodes the data. The paper defines the covert channel and analyzes its data rate, stealthiness, and robustness. In addition, the paper investigates countermeasures against the channel.