|The Difficulty of a Brute Force Attack Against MD5
The difficulty of creating two files with the same MD5 hash should be approximately 2^64. The difficulty of creating a file with a specific MD5 hash should be approximately 2^128.
This means that to replace a file with another file having the same MD5 hash using a brute force attack, you might have to make 340,282,366,920,938,463,463,374,607,431,768,211,456 attempts.
MD5's Predecessors: MD2 and MD4
MD2 and MD4 were earlier algorithms in the RSA Message Digest family. MD2 and MD4 are both currently considered obsolete. Neither have been completely broken, but both have been shown to be potentially weak.
Software Implementations of MD5