This is a CUDA program so can only be used by people with NVidia Graphics cards and CUDA SDK installed. This program is part of a paper that I'm writing on GPU in the security scene and is also my first ever CUDA program. To use the program, you must provide a wordlist (a sample wordlist is provided) and provide an MD5 hash to crack. This is quite fast, cracking over 3 million words per second on my Asus Nvidia GTS 250, Phenom x4 2Gb Ram. Feel free to comment. To build this, you must have cuda installed. The Makefile uses the default location of /usr/local/cuda, but you can modify this. Just type 'make' to build the file as 'main'. The following build options are available -DDEBUG - Will have the GPU pass back memory with MD5 registers for verification -DBENCHMARK - Will print benchmark figures -DGPU_BENCHMARK - Will benchmark the GPU kernel