Edit the php.ini file:

sudo vi /etc/php5/apache2/php.ini

Add or edit the following lines an save:

/etc/php5/apache2/php.ini

disable_functions = exec,system,shell_exec,passthru
register_globals = Off
expose_php = Off
display_errors = Off
track_errors = Off
html_errors = Off
magic_quotes_gpc = Off
mail.add_x_header = Off
session.name = NEWSESSID

Restart Apache server. Open a Terminal and enter the following:

sudo service apache2 restart