However, some program can bypass the above procedure. Like Xrumer or Zunker...
Xrumer allows to post in phpBB and PHP-Nuke (with any modification), yaBB, VBulletin, Invision Power Board, IconBoard, UltimateBB, exBB, and phorum.org.
Basically, it follows the process below:
It looks for websites where comments can be inserted.
It registers itself as a user.
It posts the message.
This type of websites usually include human verification codes, in order to make automatic registration more difficult for this kind of robots or they use filters in order to block IP addresses that carry out suspicious operations.
That? why, this program is able to recognize the texts in the images. It also allows to connect to a list of proxies in order to use different IP addresses.
To prevent posting by programs like the above examples:
1. add a hidden variable in the form to be checked: