If you don't want to advertise for hackers that your site is WorPpress powered, try to remove the meta generator tag from Wordpress.

<meta name="generator" content="WordPress 2.x.x" />

I tried more solutions but only one work properly to me.

First, locate the functions.php file in your theme. Open it and insert the following lines to the file:

// Remove WP version info
function hide_wp_vers()
{
 return '';
} // end hide_wp_vers function

add_filter('the_generator','hide_wp_vers');

If your theme has not a functions.php file, create one. Start and end the file with php tags:

<?php

// Remove WP version info
function hide_wp_vers()
{
 return '';
} // end hide_wp_vers function

add_filter('the_generator','hide_wp_vers');

?>

Save the file and reload your Wordpress page (if you use a cache plugin, clear the cache). If everything is OK the meta generator tag has been removed from the source. Check this in the page source.

Hmmm...Now you can go through all your plugins and remove the links and other garbage they interject in order to try to hide the fact that you're running WordPress.