You can also try and install Modsecurity and the latest rules.
There is also a php script called zb block that can be found here:-
www.spambotsecurity.com/zbblock.phpIf you are using wordpress for your sites then the best plan to keep them safe is to use as less plugins as you can this not only helps with security as some plugins may contain vaunarabilities but it will also help with the page speed and server load.
Also look into modsecurity also as this will help with hacker prevention.
Another tip is to add a firewall to your server like CSF.