In their native state, going back to Windows NT and moving forward, Windows operating systems include a "background service" called Messenger Service, which provides a method for network users to communicate with one another using "pop-up" messages. By design, the original intent of Messenger Service was for system administrators to notify users on their networks of system-wide events or other useful information. It was never widely employed by legitimate users. However, Messenger Service remains as a legacy feature of Windows which allows, if you are online, anyone on the Internet to actuate pop-up messages on your system. At best this includes unscrupulous spamming advertisers. At worst, malicious individuals distributing viri.

Let me make it clear that I am not talking about "Windows Messenger," "MSN Messenger," "Yahoo Messenger" or any other instant messaging program you may be using. Although it has a similar name, it is completely different from and not related to these other programs. (Although these programs also have their own security issues.) By default, Messenger Service runs quietly and unnecessarily in the background as an Internet Server, actively listening on open communication ports for incoming network packets. As it does not require being actively maintained by a system’s user, it automatically serves what ever communication is aimed at it. While it does so it is unnecessarily utilizing system recourses such as CPU cycles and Memory. So hopefully, you can see that leaving this unattended, unneeded, unwanted and almost never legitimately used "service" active on your system is not only a bad idea but as a practice, dangerous.

To sum up:
Messenger Service unnecessarily consumes systems resources which can be better used elsewhere – BAD.
Messenger Service unnecessarily provides a major security breach into your system when you are online - BAD.
And did I say that Messenger Service was unnecessary?

So at this point, most rational users will be asking themselves, "How do I get this thing off my system?" Well, the average user is not going to get it "off" their system, but they will disable it. And remember, this will have no ill effect on any other instant messaging applications you may be using.

In order to disable Messenger Service, we will explore and employ the "Computer Management" applet of Windows:
Click Start > Control Panel > Administrative Tools > Computer Management
If you have never been in the Computer Management applet before, know that this applet can be the Tech’s best friend. It contains an arsenal of tools to battle various computer issues, but for now, we will just focus on the task at hand, disabling Messenger Service.
Click Services and Applications > Services.
You will now have the "Services Panel" open that lists all of the services included in Windows. You will notice at the bottom of the Services Panel two index tabs, "Extended" and "Standard." The extended tab will make readily available the entire description that Window’s provides for each service. The list is alphabetical, so scan down until you find the listing for Messenger. Click on it to highlight it. If you have the extended tab activated, you will find the description starting with: "Transmits net send and Alerter service messages between clients and servers…." to the left of the list. If this is what you see then you know that you have highlighted the correct service.
Right Click on Messenger. This will open a drop down menu.
Click on Properties, and open the Messenger Properties dialog box.
In this dialog box, which should be open to the General Tab by default, you will find a field labeled "Service Status." Click on the Stop button. Directly above Service Status you will find the "Startup Type" drop down box. Click on the arrow to drop down three choices: Automatic, Manual, and Disable.
We are here to disable this bad boy, so Click on Disable.
Click Apply > OK.
Now, when you look at the Messenger line of the Services Panel, note that in the Startup Type Column, the word Disable appears. Good job! You are finished. You can now close the Computer Management Window.

In this exercise, we took the long way around to achieve our purpose. As in just about any other thing you may want to do with Windows, there is more then one path available to take. I choose to take you through this particular route to expose you to the Computer Management applet under Administrative Tools. A more direct route to the Services Panel can be taken by utilizing the "Command Line Interface" or "Run Dialog Box."
Click Start > Run.
In the Open line, type in "services.msc" (no quotes)
The Service Panel opens directly up without being contained in the Computer Management Applet Window.
The procedure from this point will be as previously directed, with one minor modification. After scrolling to the messenger line, rather then Right Clicking it to open the drop down menu and Clicking on Properties, just double click the line. The same dialog box appears. Is it not great how Windows has a dozen ways to do just about everything? No wonder users can get somewhat confused.

Also, while you were looking through the Services list to find Messenger service, it may have occurred to you to ask the question, "If Messenger is unnecessary, are there other services in this list that are unnecessary?" Absolutely! But whereas elimination of unnecessary services is a practical method of computer performance optimization, one doesn’t want to just go through the Services list disabling things left and right. We will leave further discussion of other services which can be safely disabled for the future.
Nuff Said!