Designed to be used with a trojan. Upload it and then run it and it'll ask for userID and password, storing them in winsys.dll in the C:Windows directory as pain text. Download that file and open in Notepad and voila you have the password.
destructive program [F-Prot]PWS-Yahoo [McAfee]Trj/AOL.Yah [Panda]Trojan.AOL.Yah [Kaspersky]
yahoo!.exe