I, and some other folks, have discovered if you try to run the Zone Alarm Pro Firewall with Security Essentials installed and the Real Time Protection enabled, anything that accesses the internet will immediately lock (freeze) the computer requiring a reboot. If I disable the Real Time Protection, things work normally.I have already advised Zone Alarm, and wanted to let Microsoft know. This may also happen with the basic Windows Defender since it was happening prior to me installing Security Essentials, or so I remember.Hopefully someone will find the cause.

Hi, Thank you for your feedback. Since we have specific support for Microsoft Security Essentials, it is also recommended that you also let them know what you experienced. Therefore, the issue could be addressed more efficiently. To contact them, please refer to the following information: Microsoft Security Essentials Help and How-to Microsoft Security Essentials Forums Thanks. Nicholas Li - MSFT

I posted this in the forum you suggested and their in depth suggestion was to uninstall Zone Alarm. It would have been nice if they would have mentioned the problem was known or was being worked on!