The most immediate risk is that the person or group distributing the crack may have embedded a backdoor. In August 2018, a massive campaign called "VPNFilter" compromised hundreds of thousands of routers worldwide, including many MikroTik devices. Experts noted that a compromised router can be used to install permanent backdoors that may survive a factory reset. If a crack grants root shell access, an attacker can leave malware, a keylogger, or a backdoor that they can use at any time to control your network.
RouterOS uses a licensing system (Levels 3 through 6) tied to the storage drive's Software ID. Because advanced licenses require a paid subscription, modified "cracked" versions like RouterOS 6.22 ISOs frequently appear on file-sharing sites. The Hidden Dangers of Cracked RouterOS ISOs mikrotik routeros 6.22 iso crack