MD4 is an hash algorithm (the four in series) created by Ronald Rivest in MIT at 1990. The hash has a length of 128 bits. The algorithm has influenced posterior design like MD5, SHA family and RIPEMD.
Based on RFC 1320.1)
Parameter: A message with length in bits ⇐ 264.
Output: The hash of the message with length in bits = 128.
For evaluating the strength of a hash function 2 concepts are in use.
Since his born MD4 has been criticized for his security even by the same Ronald Rivest because MD4 has been design thinking in performance before all. In 1991 Den Boer y Bosselaers show that MD4 without the first round are collision-weak 2). In 1996 H. Dobbertin develop a collision attack with probability 2-22 3). Also show how find message with real meaning. In 1998 he show that MD4 without one round are preimage-weak4). Since 2004 until now a lot of collision attacks has been develop 5) 6) 7) 8) 9) 10) 11) finding collisions very efficient(even with manual calculation) 12).
All this show that MD4 are very weak and nobody could use it.