- For another "UPX" format, see UPX/TPX (Photo Express).
UPX (Ultimate Packer for eXecutables) is a popular executable compression application.
UPX supports several different executable formats, including Microsoft Windows and MS-DOS. UPX-compressed executables can often be identified as such, for example by the file command.
UPX traditionally uses a data compression algorithm named UCL, though other algorithms may also be available.