You can check any number of yahoo ID's from a simple text file, and let the program check if they are online or not.
You can check up to thousands of Yahoo ids - there is no real limit. In order to send personal messages to the yahoo id's you must set up the login data under the "Login Button"
Additional you can save the Yahoo Avatar (regardless if the user is on or offline) and send them personal messages from the Program without having to open Yahoo Messenger.
Right click on an ID and choose "send Message" in order to send a personal message or save Avatar in order to save the avatar image on your local hard drive