What is a nulled xenforo forum?

[TechnoLord]

I don't understand what a nulled version of xf is. Why is it bad? What makes it nulled? Could anyone answer these questions?

 

[Slavik]

Nulled software is illegal. Not only that more often than not, while "nulling" the software, people insert malicious code or viruses into the software, so your also exposing yourself or your site to being hacked.