What is the security issue?Yes, if you are using a version of the All New Yahoo! Messenger obtained before March 13, 2007 on a Windows PC
Who is affected?Yahoo! recently identified a security issue, commonly referred to as a buffer overflow in an ActiveX control. This control is part of the Yahoo! Messenger audio conferencing code.
Yahoo! Messenger users who inadvertently view malicious HTML code on an attacker's website. If your computer has installed Yahoo! Messenger before March 13, 2007, you should install the update.
YaHoo! Secuirty Update
YaHoo! IM Blog
Source: Donna @ COU