Code injection is a type of security vulnerability that allows an attacker to introduce malicious code into a program or system. This can happen when user input is not properly validated, enabling the attacker to manipulate the application's behavior. Common forms of code injection include SQL injection, where harmful SQL commands are executed in a database, and JavaScript injection, which can lead to unauthorized actions on a website. When successful, code injection can compromise data integrity, steal sensitive information, or even take control of the affected system. To prevent code injection attacks, developers should implement proper input validation, use prepared statements, and follow secure coding practices.