FSecure is a digital signature and tamper protection system developed by PaceSoft.
It is presumably unrelated to F-Secure corporation, which didn't use that name until 1999.
Signatures can be validated using a DOS utility named FileTest.
See also SDN (SDN Project).
Little is known about the format, but it appears to work by appending some (256?) bytes to the end of the file.
- FileTest v1.00 (1992-09) - The FILETEST.EXE file itself is an example of a secured file.