Cracked plugins
Cracked, leaked, stolen, warez, or nulled plugin refers to a version of a paid plugin obtained unofficially, usually from a site dedicated to providing paid plugins for free.
It is important to note that paid does not automatically mean better.
(Dis)advantages of cracked plugins and why not to use them
Risk of malware
Cracked plugins are the most common origin of malware on servers. The malware risk of cracked plugins is without exaggeration high. If you use cracked plugins for a long time, sooner or later you will most likely be infected with malware.
You can read about how malware in plugins works and what it means for you in this section (VirusTotal and similar tools almost never detect malware).
Some hosting providers may suspend your server when malware is detected, as the server can be used for mallicious attacks (DDoS).
People won’t like it
Since most people consider the use of cracked plugins to be immoral, if you have such a plugin on your server, most people will refuse to help you in any way, whether it is a problem with a problematic plugin or not. You may be banned from asking for support, or you may be outright banned from the (support) server.
Outdated versions
Since you do not own the plugin license, you will never have access to the latest version of the plugin automatically. You will be dependent on people leaking the plugins. In case a leak of a new version is not published and you want to switch to a new version of the server that is not supported by the old version of the plugin, you’ll be stuck.
Legality
A stolen plugin is stolen software like any other, which is not legal in most jurisdictions.