Yesterday Symantec announced that they aquired IMLogic to broaden their antivirus and compliance suite to include IM platforms.
I personally think this is a very interesting acquisition as it shows that antivirus companies such a Symantec realise that as well as covering the desktop and email they also need to cover the instant messaging space as an increasing number of virus' are being transmitted through peoples buddy lists rather than their address books.
There is more information on http://www.forbes.com/feeds/ap/2006/01/03/ap2426076.html?partner=alerts including some figures from IMLogic that suggests that virus and worms threats rose 846% this December when compared to last December.
If you would like more information about securing your messaging platform, including Live Communication Server, then might I recommend you take a look at http://www.microsoft.com/windowsserversystem/solutions/security/sybari.mspx where you will find more information. I was actually in a meeting with these guys yesterday and as well as having a good understanding of the problems IM platforms face, they also have a great understanding of virus' and security in general.