In IT development work, security is everyone's responsibility. Most computer security breaches do not usually occur as a result of a single vulnerability. They happen because a breach exposes other security weaknesses to the intruder. Systems that rely on a single line of defense easily allow bad things to be done on the computer system. SQL Injection, for example, is impossible unless the user-interface fails to perform some very simple validations on the input. Every component in an application should assume that it is possible for a malicious intruder to gain access it, and take sufficient measures to prevent unauthorized penetration.