Many bots trawl the internet looking for various content management systems to exploit – how they know you’re using a particular CMS is normally easy for them to determine by looking at the source of the site – be it Joomla! or Drupal, or WordPress – when they find the version you have, they’ll start probing for known issues with older, un-patched CMSes.
Your WordPress version can be hidden by adding these to your theme’s functions.php
remove_action('wp_head', 'wp_generator');
// Remove Windows Live Writer link in header
// Do Not do this if you use it
remove_action('wp_head', 'wlwmanifest_link');
remove_action('wp_head', 'rsd_link');
// Remove WP version info
function hide_wp_vers()
{
return '';
} // end hide_wp_vers function
add_filter('the_generator','hide_wp_vers');