I am addicted to instant messengers. I admit it. I know that this admission is the first step in getting help. But I do not want to give up instant messaging, my friends, or to stop using phrases like AFK, ROFL, or LOL. What I really want help with is making instant messaging easier for me to use by programing a helpful add-in for it.

I suspect you may have the same weakness. So, in this article, I show you how to write your own add-in for Windows Live Messenger using .NET.

Beginning with version 8 of Windows Live Messenger, Microsoft has allowed users to write code, using the .NET Framework, to interact with Messenger client. By using the Messenger SDK, you can write an assembly that is loaded into Messenger and which will react to events in the messenger user interface.

Luckily for us, Microsoft has taken security very seriously in supporting add-ins to prevent malicious use. By default, add-in support is not even turned on in Messenger.

To enable it, you need to add a new registry key. The root of the key is in HKEY_CURRENT_USER\Software\Microsoft\MSNMessenger. Add a new DWORD key called AddInFeatureEnabled and set it to the value of 1. Once you do that, you can fire up your version of Messenger (as seen in figure 1):

Figure 1: Windows Live Messenger

If you look at your preferences, you should now be able to see a new Add-Ins tab, as seen in Figure 2:

Figure 2: Add-Ins Tab

At this point, don't worry too much about how to add a new add-in; we will walk through that in the second half of this article.

Even after an add-in is added to your messenger, it is up to you to enable it manually in your drop-down menu, as seen in Figure 3:

Figure 3: Turning on the Add-in

Next, when you send someone a message, the message window alerts you that you have an add-in enabled, to ensure that someone hasn't surreptitiously added an add-in for you. You can see this in Figure 4:

Figure 4: Add-In Warning

As an additional level of protection, each messenger login has its own set of add-ins to prevent someone installing an add-in that affects all users of a system. This is a separate set of add-ins for each login into Windows Live Messenger, not just for each Windows login on a machine. For example, if you and your girlfriend share a computer, and you switch the logged in account in Messenger from time to time (without actually having different Windows accounts), Messenger still prevents the add-ins from affecting both users. This is quite smart, in my opinion.

Enough showing you what an add-in looks like. Let's start writing your first add-in.