iChecker is a free application using which you can check the status of Yahoo Messenger users. Many of us like to remain invisible on Messengers so that we cannot be disturbed. Using this free utility, you can find out whether your friend is really offline or just appearing so.
The usage of the program is pretty simple. Just enter the username of your friend on the textbox and hit the Check button. The status will then get displayed. I tried the program but it produced wrong result sometimes. It is a freeware.