Well, its not too difficult to find if someone in your yahoo messegner’s friend list is really offline or invisible. Just go to http://www.ydetector.com/ , mention yahoo user id of the person(if mail id of the person is firstname.lastname@example.org then just specify tech2know), press ‘Enter’ and bingo!! The secret will be revealed :). Below is the screen shot of the same.
Stay tuned for more.