UPX 3.91 has been released. Changes include experimental support for Win64/PE To know more about this release, see the detailed changelog . Please report all problems and bugs in our bug tracker . UPX achieves an excellent compression ratio and offers very fast decompression . Your executables suffer no memory overhead or other drawbacks for most of the formats supported, because of in-place decompression. UPX strengths in a nutshell: 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 executabl...