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
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:
Add javascript code to check if data in the form is enter with key stroke.
For example:
1. add a hidden variable in the form to be checked:
2. add javascript to username input textfield:
3. add javascript code to check it before user submit the form:

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