Yahoo! Messenger is a advertisement-supported proprietary instant messaging client and associated protocol provided by Yahoo!.
Protocol Summary and Ports Range of Yahoo!
Yahoo! uses TCP port 5050 to communicate with its servers by default. It will try other common ports like 23, 21, 25, 110 ... if 5050 can not be reached. Proxy servers are also supported.
WFilter's solution for Yahoo! traffic management
Detect Yahoo! traffic in your network.
Implement a policy to block certain Yahoo! traffic.