The Messenger Service in Windows provides a framework that enables users and processes to send pop-up messages to other computers. Management applications often use the service to send pop-up notifications to administrators that an event, such as a virus detection or a backup completion, has occurred.

Windows includes the Messenger Service, but don't confuse it with Windows Messenger, the desktop conferencing application also included with Windows.

Spammers have begun using the Messenger Service to blast advertisements to unprotected users. However, you can take steps to block these unwanted messages without spending money for an application.

The best approach is to block the ports used by the Messenger Service, which prevents all traffic from entering your network. If you have a network firewall in place, block NetBIOS and RPC traffic (UDP ports 135, 137, and 138 and TCP ports 135, 139, and 445). If you don't have a network firewall, you can block these same ports with a client-side firewall.

If a firewall solution won't work for you, or if you don't need the Messenger Service, another approach is to simply disable the Messenger Service. Open the Services console from the Administrative Tools folder, and double-click the Messenger service. Click Stop, choose Disabled from the Startup Type drop-down list, and click OK. If you later need to start the service, you must change its startup type to either Manual or Automatic.