Some viruses infect programs in disk boot sectors, or the hard disk's master boot record.
Whether other types of files might be at risk depends on circumstances. For example, some files not directly executable by the user may contain code or data that the processor can execute or interpret. True data-only files cannot be infected, because they are not executable. These include GIF and JPG files, which contain data to indicate intensity and color of images. Copyright 1995-2001, The Komando Corporation.