zulhar writes:  

Recently, I wrote a guide on how to modify phpnuke captcha and has resulted in a flurry of comments and queries requesting me to write a guide on "how to change admin.php?"
Since most of hackers are targeting this critical file to achieve their mission you have to camouflage the file and secure it properly.
Read the rest of this article here for some ideas on how to secure your PHPNuke against hackers...