One the ways that you can make hacking your server harder is by hiding the version of software that you are using so hackers don't know if your server is exploitable with an specific exploit or not.

2 ways that we can do that is hide the php and apache version.

if you have tried to add this these lines to your server to hide the apache and OS versions and if failed even after restarting apache.

ServerSignature Off 
ServerTokens Prod

You might want to remove them add add them to /etc/apache2/conf-available/security.conf

and change the expose_php = Off in /etc/php5/apache2/php.ini

Restart apache server for changes to take effect.

service apache2 restart