Hydra is a powerful tool for conducting brute-force attacks against various protocols, including SSH. It is capable of using multiple threads to perform concurrent attempts, significantly increasing the efficiency of the attack. This capability makes Hydra particularly suited for brute-forcing user passwords over SSH, as it can quickly try numerous combinations of usernames and passwords. The tool's ability to support a wide range of protocols, its flexibility in handling different authentication mechanisms, and its efficiency in managing multiple simultaneous connections make it a go-to choice for penetration testers looking to test the strength of passwords in a target system's SSH service.