I use a Server 2008 R2 Enterprise machine which is used solely to allow my customers to remotely connect using remote desktop connection. When they log in, the application is started and when the close the application they logged off the server. They never see a desktop (drive mapping is turned off my default, so they need to ask me for that feature if they need it) or anything other than my application.
I'm looking for recommendations on a basic antivirus program to protect the server. I'm currently using Microsoft Security Essentials. I'm not sure, given the limited access given to my customers if something more powerful than MSE is needed.