Help! My Codeigniter site was hacked

[eluser]gfields[/eluser]
Thank you PhilTem, I'll follow your golden rules but - more specifically - is it possible to avoid that, simply appending code to the uri, someone can cause all these troubles?

I found this code to put in the htaccess file:

RewriteCond %{HTTP_USER_AGENT} libwww-perl [NC]
RewriteRule ^ - [F]

What do you think? Can it be useful?

ps: ok, it's not php injection but how can i call it? htaccess injection?