Windows only: Lock down your PC and prevent unauthorised executable files from running with freeware application Trust-No-Exe. As the computer's administrator, you can set up a whitelist of clean executable files that you will allow to run and selectively block others. Once installed, Trust-No-Exe adds an entry to your Control Panel, from which you can tweak your whitelist and blacklist. If you're heading home to fix your mum and dad's computer for the seventh consecutive year, you might want to add this to your Thanksgiving rescue kit. It's not foolproof, but it could be a worthwhile deterrent. Trust-No-Exe is freeware, Windows only.