The level ProxyMania based on sql injection.
your mission is to find out the real ip of the person
who used the proxy.

As you can see , the last member is Robbert and the
admin might be BILL.
It is simple to get access into the last member account...

The next step is to understand what you can do as 
Robbert and what you can't do- and change it to can.
Of course robbert is not the user you search for , he
is only giving you more options.
And you don't need to find other members , only IP.