Certified Information Systems Security Professional (CISSP) Practice Exam

The primary function of a boot sector virus is to ensure that the virus loads upon system startup. Boot sector viruses target the boot sector of a storage device, which is the area responsible for initiating the operating system when the computer starts. By embedding itself in the boot sector, the virus can execute its code before the operating system is fully loaded, allowing it to take control of the system as soon as the computer is powered on. This early execution often enables the virus to spread and perform its malicious activities before any security measures can be activated.

In considering the other options, options related to encrypting data files, executing commands remotely, or monitoring user activity are not specific to the nature of boot sector viruses. While a boot sector virus may have the capability to perform various malicious actions once it is running, its primary defining feature is its method of infection and activation at startup, which sets it apart from other types of malware.