Making an admin script

[DEFCON1]

Hi,

I think about making my own little admin script.

With everything I read: Lua viruses, net messages backdoors... I've heard even ULX had backdoors (but when an exploit is known, it is quickly fixed), so I'm affraid that if I make my script, it will be easily exploitable because I don't know about security...

So do you have some pro tips ? What should I know about security, exploits? Also if you could explain how it is possible that [url=http://facepunch.com/showthread.php?t=1386255]a Printer addon can allow someone to make himself an admin[/url] :/

Thanks in advance.

[Jeezy]

Sanitizing client input is one way to start.
This page demonstrates what I mean.
[url]http://en.wikipedia.org/wiki/Secure_input_and_output_handling[/url]