You can install Microsoft Security Essentials on Server 2012, below is how to do so.
- Download a copy of MSE from Microsoft: http://windows.microsoft.com/en-us/windows/security-essentials-all-versions
- Right Click on the mseinstall.exe
- Click on Properties
- Click on the Compatibility tab
- Locate the Compatibility section
- Check Run this program in compatibility mode for
- Select From the drop down menu Windows 7
- Open a Command Prompt as Administrator
- Navigate to your Downloads folder (ie. cd C:Users%username%Downloads)
- Run mseinstall /disableoslimit and follow the installer prompts to install MSE on your Windows Server 2012.