Executable compressors work by compressing selected
portions of executables. At runtime, compressed
executables are decompressed and reconstructed directly
into their virtual image (memory) so that no data is ever
written to the disk. The executable can therefore be run
exactly as it was before without the user even knowing it
was compressed.
PECompact2 is a next generation win32 executable/module
compressor. Commonly termed an 'executable packer', such
utilities compress executables and modules (i.e. *.EXE,
*.DLL, *.OCX, *.SCR). At runtime the compressed modules
are rapidly decompressed in memory.