Upack is a packer that can compress Windows PE file, which may self-decompress and run normally without any other decompresser.

It can pack executable files of Windows PE format files with almost the best compression ratio. Whereas DOS-EXEs(MZ), Win3.x-EXE/DLLs(NE), and any other platform programs are not supported by Upack. Upack is only for compression, not for protection mainly.