SQL Injection

Definition:
 An SQL injection is a computer attack in which malicious code is entered in a poorly designed application and then passed to the database. The malicious data then produces database query results or actions that should never have been executed.

Why someone would use it:
 Hackers frequently use SQL injection as a means of attacking and taking over databases. They could use this to and find their password log in to someones account

Examples:
 ' OR EXISTS(SELECT * FROM users WHERE username='user1' AND password LIKE '*w*') AND ''='
 The above code would find if the letter w was in user1's password.