This indicates an attempt to access Yahoo! Messenger.
Yahoo! Messenger is an instant messaging client provided by Yahoo!. It is an advertisement supported IM client and it free of charge. It also uses its own proprietary protocol to communicate with the server. A generic Yahoo ID can be used to access Yahoo! Messenger. The same ID can be used to access almost all other Yahoo services. Among the services offered by Yahoo! Messenger are chats, SMS-es, file transfers, voice calls, and video calls. Yahoo! Messenger is supported on the Android, iOS and web browser clients.