Stealth & Privacy Settings
Control who sees you online. Block unwanted IMs too.
Stealth settings provide you more control over your time in Yahoo Messenger, by allowing you to choose which friends see you as online or offline.
If you want to sign in but not let your friends know you're online, select the "Sign in as Invisible" option at log in. Once you're signed in, you can see which of your friends are online but they can't see you. You can still send and receive messages, even if you appear offline.
If you are already signed in and want to become invisible to your friends, change your status to "Invisible to Everyone". This will instantly make you appear offline to your friends.
To appear online to some friends but offline to others, use individual stealth settings to designate which friends should see you online. You can access individual stealth settings by right clicking on a friend in your contact list. You can also appear invisible to an entire group (e.g. co-workers). Individual stealth settings are only available in the following versions of Yahoo Messenger: 9.0, 10, Mac.
How to handle unwanted messages
Instant Messaging is a fun and timely way to connect with the people you know and trust. But sometimes, those outside your circle of friends may try to contact you and start a conversation. If you receive an unwanted message from someone, you can click the "Ignore/Add to Ignore List" button in the IM window to permanently block their messages. At that time you will also have the option of reporting the message as spam. The user you're blocking will not know that you have chosen to ignore their messages.
Reporting spam in Yahoo Messenger works the same way. If you receive an unwanted IM from a user, you can click the "Report as Spam" link. This will also add that user to your ignore list.