Mobile ad hoc networks are widely used networks in the present times. The nodes in such network consist of laptops, mobile phones etc. These devices often have very important information in them. Security of these networks is very vital. These networks are prone to various kinds of attacks such as black hole attack, wormhole attack, DDoS attack etc. Out of many other attacks possible, black hole attack is pretty dangerous as it drops all the packets received by it. This paper presents various studies that have been done by many authors in the past regarding detection and prevention of such attacks.