Lock It Down!

(WARNING: One wrong move could lock you out of the system directories completely, rendering Windows unbootable. Before and after employing this method, I recommend backing up your hard drive with Acronis True Image. You should be doing this anyway; even if you never get infected, every hard drive fails eventually. Order your copy today, and preserve not just your current settings in Windows, but the entire system. The most secure computer is one that is backed up.)