Which of the following is NOT a type of COMSEC?

In the context of Communications Security (COMSEC), the goal is to protect classified and sensitive communications from interception and exploitation. The types of COMSEC measures can include encryption devices, secure voice communication systems, and secure transmission protocols.

The KG-84, ANDVT, and JOSEKI are all recognized types of COMSEC systems or devices. The KG-84 is a type of encryption device used primarily for securing voice and data communications. ANDVT, or the Advanced Narrowband Digital Voice Terminal, is a secure voice communication system used by the military to provide encrypted voice communications. JOSEKI, although less common, refers to a secure digital communications system utilized for maintaining secure channels.

In contrast, XCOM does not refer to a specific type of COMSEC system or device recognized in the same context as the others listed. Therefore, this makes it the correct answer to the question regarding which option is NOT a type of COMSEC. Each of the other options has specific roles within the realm of secure communication.