With the advancement of technology everyone is using computer and web applications. These web applications can be easily made by using rapid application development environments by developers. But they do not consider security aspect necessary in the process of providing attractive functionalities & also they are not experts in that field. This make web applications vulnerable to several attacks. Among these attacks SQL injection is considered most dangerous vulnerability. This paper describes various approaches used by authors to prevent SQL injection attack using various methods like intrusion detection, black box testing etc.