Software is broadly divided into system software, which manages and maintains the computer, and application software, which lets a user perform specific tasks such as writing documents or browsing the internet. Within system software, a smaller category called utility programs exists to perform maintenance and support tasks that keep the computer running smoothly, such as compressing files, managing disk space, or scanning for malicious code.
Anti-virus software fits squarely into this utility category because its job is to protect and maintain the health of the system by detecting and removing viruses, rather than helping the user complete an everyday task the way a word processor or spreadsheet would. It is not an operating system, since it does not manage hardware resources or run other programs, and it is not a translator, since it does not convert one form of code into another.
When classifying software, ask whether its purpose is to support and protect the system itself; that purpose is the hallmark of a utility program.
