The NFO reference article from the English Wikipedia on 24-Apr-2004
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NFO

NFO is an abbreviation of INFO which is an abbreviation for INFORMATION. In Microsoft Windows, a file with a *.NFO extension is opened with System Information (a program).

Commonly, files with the *.NFO extension are not designed to be opened with System Information, but with a text editor or specially designed NFO viewers. These files are usually associated with software cracks/patches where the credits and information is stored. Usually, these files, once viewed with a text editor, have a large ASCII art logo at the top and information about the software crack/patch following the logo.