The symptoms described by the employees, such as systems being very slow, restarting automatically, and experiencing frequent hangs, are indicative of a security incident involving malicious code. Malicious code refers to software or scripts designed to cause harm to a computer system, network, or server. In this case, the virus that forces systems to shut down automatically after a period of time is a type of malicious code. It disrupts the normal functioning of the system, leading to decreased performance and unexpected behavior.