source: http://www.securityfocus.com/bid/23876/info

Advanced Guestbook is prone to a local file-include vulnerability because it fails to properly sanitize user-supplied input.

Exploiting this issue may allow an unauthorized user to view files and execute local scripts.

Advanced Guestbook 2.4.2 is vulnerable to this issue; other versions may also be affected. 

http://www.example.com/../../../hack_www/htdocs/hack