Yahoo with firewalls

I'm running a firewall (<A HREF="http://www.kerio.com" target="_new">Kerio</A> ), and Yahoo Instant Messenger plays complete havoc with it. I create rule after rule allowing it access to various sites through various ports, but it always wants more access, and eventually I end up giving it free reign to open as many ports as it wants.

Obviously I'd prefer a more secure way of doing this. Does anybody know the minimum amount of access I need to give Yahoo in order to run properly?

Thanks in advance to the legions of die-hard Forum-goers who rush to my aid