Cracking

Cracking could describe either,

1. the process of cracking passwords, through various methods, which may include brute force attacks and dictionary attacks.
2. the process of cracking software, to bypass software registration, allowing full use of software without having paid.

Both activities are illegal, unless given express permission to do so - cracking a password would likely be against the password system's terms of use, but would never the less provide access to an unauthorised computer system, which would be in contravention to the Computer Misuse Act. Software companies would be required to test both password entry systems, and resilience to software cracking.