Yahoo messenger allows stealth mode using which you can set your online status as “offline†even when you are logged in to yahoo messenger. People use it to avoid chat when they are busy or to block out spam messages.
1. But there is a hack which allows you to see whether someone is really offline or not. The easiest way is to directly acess the online status image using the URL – http://opi.yahoo.com/online?u=userid&m=g&t=2 (replace userid with the actual user id).
2. The second way is to start a voice chat with the userid you want to check. If you don’t get an error it indicates that the user is indeed online, but in invisible mode. This works only in previous versions of Yahoo messenger.
3. The only method which seems to work on latest versions of Yahoo messenger is the IMEnviornment hack. First send a message to the user id and then immediately change the IMEnviorment. Now if the guy is really offline, you will get a message “waiting for your friend to load the theme†message. If he is online, you will just get a blank page!
Or you can use our Yahoo Invisible detector .