The .unknown file extension is often used by some data recovery tools for flagging files that have not been completely recovered. This UNKNOWN file format may also be used by a few data recovery tools for flagging files that have been corrupted beyond repair. These .unknown files may not work properly, even when opened using an application that has support for its original file format.The UNKNOWN file format may also be used by certain download management programs and P2P (peer to peer) file sharing tools. Files that have not been completely downloaded may be appended by these applications with the .unknown file extension. These UNKNOWN files may be converted by these download management and P2P applications into its original format as soon as the download has been successfully completed.It's best to leave these .unknown files alone, especially if the file is sent via email from an unknown source. Certain Web browsers may also flag incomplete download items as UNKNOWN files during the download process.
Try a universal file viewer
File.org aims to be the go-to resource for file type- and related software information. We spend countless hours researching various file formats and software that can open, convert, create or otherwise work with those files.
If you have additional information about the UNKNOWN file format or software that uses files with the UNKNOWN suffix, please do get in touch - we would love hearing from you.