Windows 2000 and Windows XP have a feature which allows network administrators to communicate with their users. It's called Windows Messenger, not to be confused with other programs such as MSN Messenger or AOL Instant Messenger.

The problem with it is that it can be used to send unwanted spam messages across the Internet to any user. The messages appear in the form of a pop-up which would look something like the following:

Such messages can be extremely annoying or worse. They can contain explicit language or direct anyone who clicks on it (even to get rid of the message) to web sites containing objectionable content. The best thing to do is disable them, and here's how.

From the desktop of your computer, right click on My Computer and choose manage. The computer management window now opens:

Expand Services and Applications by clicking on the plus sign. This will display the services installed on your system.

Select Services and scoll down until messenger is displayed.

Right click on it and select Properties.

Under the Service Status section, click Stop. The service will now stop, you will see this happening on the screen and it may take a few seconds.Then under Startup Type choose Disabled.

This should prevent future pop-ups of this type. If the pop ups are still coming, they are being generated in a different manner. Try downloading a free spyware detection program such as Ad-Aware, and run it on your system.