A code-injection developer is typically involved in identifying and exploiting vulnerabilities in software applications, often for security testing purposes. They inject malicious or testing code into a system to manipulate its behavior, identify weak points, and test security measures. This technique can expose potential threats and risks, allowing developers to fix issues before they are exploited by malicious hackers. Code-injection can be used in various types of applications including web, mobile, and desktop. It's important to note that while code-injection can be used for ethical hacking, it can also be used maliciously, hence necessitating robust security measures.