How To Get Firebird / Interbase Connected Users

In some tasks we need to know how many users are connected to the database. And even which users are connected… There is an interesting piece of code with which you may achieve this this. It is an additional source file written for ZeosDBO 6.1.3 library. It only works with Firebird 1.5. But it can be easy modified for another Firebird/Interbase server.