The number of gangs which have fearsome reputations is extensive and the crimes they commit often go under the radar and are not punished. Other groups also operate from inside jails

A list has been compiled of he world's 20 most feared criminal underworld gangs.  These criminal organisations have the most dangerous reputations and include notorious names like the Hells Angels, Aryan Brotherhood, Russian Mob, MS-13 and Triads.