File extensions are attached to file names to let the computer know which program should be used to open a file. .ICO files hold images that Windows uses as icons. (reference 2) Icons are commonly used to identify files or folders on the computer. (ref 3) .ICO files are frequently opened using Windows Fax Viewer or Windows Photo Viewer. (reference 1) However, if they cannot be opened automatically, users can download software to open an .ICO file.
