A legitimate voice or video communication application modifies data in a communication session to produce a watermark. The watermark is a piece of information that is part of a communication session that is not readily observable, but can be verified later on. The purpose of a watermark is to verify that the communication session is a legitimate communication session and does not pose a security breach. The video or audio communication session is monitored for a watermark. In response to determining that the communication session contains the watermark, the communication session is allowed continue. In response to determining that the communication session does not contain the watermark, the communication session is identified as a potential security breach. If the communication session is identified as a potential security breach, the communication session can be dropped and a user can be notified of the potential security breach.