It is not obvious to a user when a jar has been blacklisted. There are 3-4 different scenarios and depending on when the jar is loaded you can get different exceptions, etc. You usually have to enable tracing in the console to see if the jar has been blacklisted.
We should create a consistent security dialog message that indicates when a jar has been blacklisted. We should also add some sort of message indicating that the user should contact the vendor or publisher for more information.