Use Cases

So the purpose of a Use Case is for an 'Actor' to successfully complete a 'Goal'. Fair enough. But... what if you have a Use Case like the following:

Name: Hacker Compromises The Site
Primary Actor: Hacker
Success Criteria: Hacker obtains unauthorised access to the site
Failure Criteria: Hacker cannot obtain access to the site

Is this a valid Use Case for your system and, if so, then is a Success actually a system Failure? Is this just a logical paradox or a real problem? Would you just word it as follows instead?

Name: Prevent Site Hacking
Primary Actor: Hacker
Success Criteria: Hacker cannot obtain unauthorised access to the site
Failure Criteria: Hacker obtains unauthorised access to the site

Is this just sidestepping the problem? Is it not a good Use Case because the goal should always reflect the success criteria of thePrimary Actor?

Answers on a postcard please. Or just a comment will do :)