Messenger is a service that comes with Windows XP, NT, and 2000. Advertisers have taken advantage of this by sending ads over this service. Messenger Pop-up Blocker is a free program that blocks 'messenger pop-ups' from appearing on your desktop. It does not block other pop-up ads while surfing the Internet. Messenger Popup Blocker does not in any way disable you from instant messaging (AIM, MSN Messenger, ICQ).