The person that pays the bills is liable. If that said person involves others, it is at his discretion, however he pays the bills and ultimately the buck stops at him. Ignorance of what is going on is not an excuse.

If for example you host a warez site in america, or a cracking forum, or any site that is not in accordance with the DMCA, usually you will be asked to close the forum more than once, and be given very certain time-frames in which you can do so without any repercussion.

Choosing to ignore these is where you start getting into warm water. If you make some bad moves, the water is only going to get hotter. This is the point where most people fall foul and end up in trouble.