Even if a nulled plugin somehow arrived free of injected malware, you would still be sitting on a ticking time bomb. Premium plugins rely on a valid license key to authenticate with the developer’s update server. When you’re running a cracked copy, that connection is severed. You won’t receive version updates, bug fixes, or—most critically—security patches.
if you aren't paying for the product, your security usually is. specific security risks of using nulled plugins or perhaps find some legitimate free alternatives to Optinmonster? Optinmonster Pro Nulled