Using a cracked serial number is software piracy. It is a violation of copyright law. While individual users are rarely pursued in court, it is important to understand that circumventing the software's protection is illegal. Furthermore, if you use a pirated version for business purposes, the legal liability becomes significantly higher, as commercial use explicitly requires a paid license.
If you are concerned about security—or if you want software with different features—there are excellent open-source and free alternatives: Serial Number Daemon Tools Lite 10.1.0.74 LINK