This happens most often when a floppy disk is left in the disk drive of a computer and then the computer is turned on or rebooted. A file infector is a virus that attaches itself to, or is associated with, an executable file. The infection can also spread to executable files, which are run from writable floppies on an infected computer. The infection is usually spread to other computers by sharing infected executables. Antiviral software attempts to prevent, detect, and remove viral infections.
Most antiviral software uses, or makes available, all three.
This allows you to keep track of activity that you may not be aware of and to determine whether you want the activity to continue or be prevented. Common areas that are frequently checked this way are the memory map, what is loaded into memory and where it is, and executable file sizes. More often than not these items are relatively static and most unexplained changes should be investigated. Scanning is the lynchpin of most antiviral software. When a signature is discovered the application notifies you of the possible presence of a virus.