Choose “Invisible” when you want to appear to be offline on Yahoo! Messenger. This option allows you to continue IM and audio/video chats with the users you wish to converse without appearing available to others. [Note: Members to whom you appear offline to can still send you IMs, which would regularly be saved in your offline messages. They will receive a message that you are offline and will receive their IM when you sign back in, despite having already received the message.]
The “invisible” option can also be activated by pressing Ctrl+Alt+I.
Reproduced with permission of Yahoo! Inc. ©2008 Yahoo! Inc. YAHOO! and the YAHOO! logo are registered trademarks of Yahoo! Inc.

