Instant Messengers have a feature to change the current status of the active user. The different statuses range from available over do not disturb to invisible. The Instant Messenger contacts see the statuses of their buddies unless the status has been set to invisible. Invisible means that the user is online but showing as offline [...]

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Most Instant Messengers offer a function to hide your real status from your contacts and buddies by showing a faked offline status. People use it mainly to be able to work uninterrupted.

There is however a way to find out if your Yahoo contact or buddy is really offline or only faking that he is offline. It basically lets you detect if they use the invisible mode in Yahoo Messenger.

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