UPX – Ultimate tiny packer for any eXecutable file

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UPX (short for Ultimate Packer for eXecutables) is a classic, illustrious universal and extendable lightweight packer for various executable files (such as EXE, DLL). With excellent compression ratio and very fast decompression speed. And can be regarded as a commercial quality freeware!

UPX supports executable file formats on almost any platform, such as DOS, Windows, Mac OS X, Linux, BSD, etc. It has very good compression ratio (compressed executables dwindle 50%~70% in size). And more important, the executable or library file compressed by UPX does not loss any function, they can run normally just like before. In fact, UPX has not adverse effects on running time or memory usage for most of the supported file formats.

In addition to being used to compress the executable file to save a lot of storage space, UPX has another infamous and main purpose – packing (add a shell) trojans and viruses (a common way of protecting executable files). The packed executable program can be run directly, but does not allow to view its source code (unless unpack the shell first) – so as to avoid killing by antivirus software easily.

// Key Features //

  • excellent compression ratio: typically compresses better than WinZip/zip/gzip, use UPX to decrease the size of your distribution!
  • very fast decompression: ~10 MB/sec on an ancient Pentium 133, ~200 MB/sec on an Athlon XP 2000+.
  • no memory overhead for your compressed executables because of in-place decompression.
  • safe: you can list, test and unpack your executables. Also, a checksum of both the compressed and uncompressed file is maintained internally.
  • universal: UPX can pack a number of executable formats.
  • portable: UPX is written in portable endian-neutral C++.
  • extendable: because of the class layout it’s very easy to add new executable formats or new compression algorithms.
  • free: UPX is distributed with full source code under the GNU General Public License v2+, with special exceptions granting the free usage for commercial programs as stated in the UPX License Agreement.

// Prompts //

  • This is a DOS-like program, that means you can and have to operate it in the command line.

// Download URLs //

License Version Download Size
Freeware Latest n/a

(Homepage | GitHub)

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