MD5 was a cryptographic hash function that generated a 128 bit output. It was designed in 1992. But since then weaknesses in the collision resistance have been discovered, which make MD5 unsuitable for almost all use cases.
Furthermore MD5 is an extremely fast algorithm that can be speed up even more on graphic cards. MD5 is therefore not suitable for hashing passwords anymore.
Research papers concerning the weaknesses of MD5:
- The Status of MD5 After a Recent Attack Dobbertin, Hans (1996)
- How to Break MD5 and Other Hash Functions Xiaoyun Wang; Hongbo Yu (2005).
- MD5 considered harmful today - Creating a rogue CA Certificate