The NFO file extension is used for a Warez Information File developed by THG. What Is an NFO File? NFO files are typically associated with media downloaded using a distributed file network, such as BitTorrent, or through a. What is an NFO file? Data file used by Microsoft's System Information tool, a Windows software utility for gathering system information and for diagnosing problems;. nfo file will, by default, attempt to open the file with the System Information tool, and it will fail to do so because it isn't designed for that use.