Random 20 second Freezes

In that case I would uninstall MSE, reboot and install Avast for comparable protection without any performance hit. MSE can cause issues on rare occasion. I'm surprised these weren't resolved when you reinstalled it which we have users do all the time here without any issue.

Defender is adequate protection, using the same definitions as Defender in Win8 which is a renamed MSE. But if you don't trust it then use Avast which has always been the second-most recommended AV for performance and adequate protection here.

You can get email support for MSE at it's website.

Since you're a comprehensive enthusiast look over these same steps for a Clean Reinstall - Factory OEM Windows 7 which compile the tools and methods which work best based on tens of thousands of installs we've helped with here.

Thanks Gregrocker for these suggestions!! If you can answer the following, I’d appreciate it:
1) I had heard that Defender in Win 7 was only for anti-spyware but not anti-virus. Is this not true? Does it really offer the same protection as the MSE that is native to Windows 8?
2) Does AVAST have a simple unobtrusive GUI? The simple unobtusive GUI in MSE is the main reason I liked it but due to the Freeze issue I am motivated to try something else.
Thanks again for your suggestions and the Instructions for Clean Reinstall!

Here is a brief follow up. I uninstalled MSE and installed Avast Free AV. I could not repeat the problem with Avast Free AV installed. This further supports the conclusion that MSE or the combination of MSE with Windows 7 is responsible for the Freeze described in the opening post. Hopefully someone else will find this information useful. My thanks to those who helped out with this.

Six days ago I updated all three of my Windows 7 computers with this problem to the newly released Microsoft Security Essentials Ver 4.3.219.0. Presto, no more freezes since that time on any of the three machines! The computer detailed in ‘my system specs’ was built over three years ago and has had this freeze problem with each new release of MSE for that entire time except for the latest release of MSE. The other computers are not as old but have also had the problem with MSE until the latest release. That’s quite a long time to go without a fix. Hopefully the problem won’t return on a subsequent release of MSE! :)