Nulled means makes it illegal .For example 'X' bought a vbulletin license and he cracked it made it illegal and shared with so many people. Here he nulled the script.
Now their is so many sites who gives (warez Sites ) nulled scipts.And here gdi ask whether he can install those nulled scrpits in the host we offer for them.
He is right most of the time these scripts are ok but if you got your script from hacker it might contain a malicious peice of code that will reveal everything to him
This is illegal so it is not allowed in any host, also in this one. So i can say: GDI you are not allowed to install nulled, cracked or whatever software, that you didnt bought (i'm talking about shareware soft)