Because you aren't using an official license, you won't receive security patches. A forum running on 2012-era code is already vulnerable; adding a compromised theme makes it an easy target.
Nulled files are notorious for containing obfuscated PHP code. This can allow hackers to gain administrative access to your server, redirect your traffic to malicious sites, or steal your users' emails. Woltlab Burning Board 3.1.7 Nulled Theme
Released over a decade ago, Burning Board 3.1 (codenamed "Volcano") was one of the most powerful community platforms of its era. Version 3.1.7 was a stable maintenance release that many administrators loved for its deep customization, "WoltLab Community Framework" (WCF), and its iconic, structured forum layout. The Problem with "Nulled" Themes Because you aren't using an official license, you