Which type of virus requires the user to perform an action for infection?

A macro virus requires the user to perform an action for infection because it is typically embedded in documents, such as those created by Microsoft Office applications. When a user opens an infected document and enables macros, the virus executes, leading to potential damage or unauthorized actions. This type of virus exploits the macro functionality commonly used in productivity software, making user interaction essential for its spread.

In contrast, a boot sector virus infects the master boot record of a storage device and typically activates when the computer is booted up. An encrypted virus uses encryption to hide its code from antivirus software but does not necessarily require user action to infect. Similarly, a polymorphic virus changes its code as it spreads to evade detection but does not rely on user actions to infect systems. Thus, the macro virus is distinctly characterized by its dependence on user actions to trigger its malicious activities.