What's the difference between Windows Live Messenger, Windows Messenger, MSN Messenger, and Windows Messenger Service?

Windows Live Messenger (WLM) is the latest and greatest version of Microsoft's instant messaging client. Very much like Yahoo instant messenger (YIM), or AOL instant messenger (AIM). Anyone running Windows XP can download Windows Live Messenger and begin IMing with other users.

WLM has a slew of new features compared to its previous versions - the most interesting to me is the ability to share folders with people you're chatting with. WLM promises to interact directly with Yahoo Messenger in the near future.

WLM is actually version 8. Version 8? Yes, because it is really just a new name for, the latest version of and the replacement for MSN Messenger.

It's the same program with a new name, and new features.

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MSN Messenger is simply the "old" version of Windows Live Messenger - nothing more, nothing less. Versions 6 through 7.5 all seem to be popular and "in the wild".

If you have Windows XP, you probably want to upgrade to the latest version: Windows Live Messenger. If you're running any other version of Windows, you may need to stick with these older versions of MSN Messenger.

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Windows Messenger is yet another instant messaging client, very much like MSN Messenger and WLM. It comes with Windows XP and runs only on Windows XP. It's typically version 4.7, though the updated Windows Messenger 5.0 also runs on Windows 2000, and can be downloaded here.

Important: Windows Messenger is not MSN Messenger, nor is it WLM. That's important because you can run Windows Messenger at the same time as MSN Messenger or WLM. That can get confusing if they are both logged into the same account because a message about being logged into two places may result.

Windows Messenger is a different program from the other two. It has a different feature set, and release on a different schedule. In particular, Windows Messenger is more tightly integrated with applications such as Microsoft Exchange, Microsoft Outlook, Microsoft Outlook Express, or the Remote Assistance feature of Windows XP. The differences, and the confusion, don't end there, though. Microsoft has a Knowledgebase article that touches on more of the technical differences, and provides instructions for installing and running both on the same machine. The good news is that chances are, you'll never need to know how, or why, you would want to.

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Windows Messenger Service adds to the confusion. It has a similar name but it is completely unrelated to everything I've talked about so far.

On Windows 2000 and Windows XP there is a service, called "Messenger", often unfortunately referred to as the "Windows Messenger", that is used to present what can best be called "network messages" to a machine's user. This is not an instant messaging application, but rather software that runs in the background, listening for incoming messages, and popping up a very simple box containing the message when one arrives. The most common example might be in a corporate environment when you send a document to a network printer. The messenger service handles the pop-up message that the printer sends back when it has finished.

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So what, of all of that, do you actually need or want?

My recommendation is actually very, very simple:

• Windows XP users should download Windows Live Messenger and use it.

• Folks without Windows XP should stick with their existing version of MSN Messenger, or perhaps download and run a third-party application such as Trillian. (It's unclear at this point if Microsoft has an official recommendation for non-XP users.)

• Everyone should uninstall Windows Messenger. Most people simply have no use for it.

• Everyone should disable the Windows Messenger Service. Again, there's simply no need for it.

The bottom line? For Windows XP users, all you need is Windows Live Messenger. Ignore or uninstall everything else.