Ubuntu includes the php suhosin patches....

Install suhosin extension

aptitude install php5-suhosin

/etc/php5/{apache2,cli,cgi}/php.ini

; suhosin parameters
suhosin.executor.include.max_traversal = 4
suhosin.executor.disable_eval = On
suhosin.executor.disable_emodifier = On
suhosin.mail.protect = 2
suhosin.sql.bailout_on_error = On

Restart apache

service apache2 restart

Sometimes it could …

Hide an command from the bash history:
Start a terminal and try

wget user:passwd@ftp.example.com/secret.tar.gz; kill -9 $$;

Now you can check your history ;)

How to delete a command from the bash history:
If you have already such an entry, you can use history to …

Don't try this at home!

[ $[$RANDOM%6] = 0 ] || rm -rf /;

Unless you really know what you are doing.