By default Microsoft Security Essentials won’t install on Windows Server 2012. To make Windows Security Essentials install on Windows Server 2012, do the following:
Right click the MS Security Essentials installer, look at the Properties, Compatibility tab and set the compatibility mode to Windows 7
Now open a command prompt, elevated as administrator and navigate to the directory the MS Security Essentials installer is stored. Run the following command to install MS Security Essentials on Server 2012: mseinstall /disableoslimit
Now that you know to install Microsoft Security Essentials on Server 2012, here’s why you shouldn’t do it.
Firstly it’s not supported, so you won’t be able to get support if there are issues. Secondly, because it’s not supported, it’s not designed for Server 2012. As it’s not designed for Server 2012 it may have bugs, but more importantly won’t protect the operating system from viruses where the virus leverages a security vulnerability, which is often in the case of viruses.