Final answer:
A virus that infects an executable program file is known as a program virus, which becomes active when the infected program is executed and can spread to other executable files.
Step-by-step explanation:
A virus that infects an executable program file is known as a program virus. This type of virus integrates itself into the executable files of a program. When the program runs, the virus is activated and can replicate and spread to other executable files, potentially causing harm to the system's data and affecting its performance.
Viral infection in computers can also be due to other types of viruses, such as a macro virus which is embedded in documents, a companion virus which adds a malicious executable to an existing program, or a boot sector virus that infects the master boot record of a storage device.
Understanding the differences between these types of viruses helps in creating effective strategies for prevention and removal, thereby maintaining the health of the computer system.