An attacker can use this practice by sending a fake header that contains a domain name. For example, it can be used to corrupt the web cache or password reset emails. Follow this procedure to prevent a host header injection attack on Decision Center and Rule Execution Server. THC Hydra is a powerful tool to use against login forms. It can perform brute force and dictionary attacks against different types of applications and services. When a web application relies on usernames and passwords as its only line of defense, a pentester or a malicious user can use Hydra to perform a dictionary attack against it.