MD5-Hashs are used for global error checking of MPC files.
It is also used to identify identically source files.
A MD5-Hash is a cryptographic one way hash which generates a 128 bit hash from a list of blocks with 512 bits. It should be from the computational effort impossible to generate an articifial file from a given MD5 hash.
Method of computation is defined in RFC 1321. Computation speed is similar to the well known but very weak CRC-32.