A lot of people become nervous (and understandably so) when checking their auth or security logs, in Centos /var/log/secure and see dozens, hundreds of even thousands of attempted logins to various services, especially SSH.
Of course you could manually block these people/IPs but no one has time to read the logs like that, what if some program or script could do it for you?
This is what denyhosts does for you, it checks the logs and based on a certain number of failed SSH attem........