Check out this yahoo status checker and send an email at contact [at] yahoostatuschecker.com Specify that you need an invisible checker script.
Most of the scripts just leach the results from real working websites. The real script that does the actual checking is very complicated. The method involves sending the target a fake signal that your avatar has changed. Yahoo messenger client will react to it by trying to grab the new image. This can be detected.
The real script code source it's available for free downloand, and they are more methods to detect if somebody is online or offline
thanks but no thanks, you are only trying to add another link to your website. If you don't want to help than stop posting spam replyes with nothing useful in them