Windows users who have previously used the famous Avast antivirus may know about this feature. When the feature is enabled, Avast scans your system during system idle time. In other words, when the system is idle, Avast screensaver starts and performs the above mentioned tasks in the background.
If you are a Microsoft Security Essentials user and want to get this cool feature in MSE too, here is the solution. Jwils876 from Deviantart has created a screensaver which is pretty much similar to the Avast screensaver.
How to use:
1. Download the screensaver from here. Extract the contents to a folder to see two screensavers. Right-click on a screensaver (the NG or No Graphics screensaver will update and scan silently with hidden CMD prompt ) and click install to install the same.
2. Right-click on desktop, select Personalize and then click Screen Saver option to open Screensaver dialog-box. Make sure that the MSE screensaver is the default screensaver. Here, you can change the default wait time to your desired one.
3. From now onwards, when the system is in idle sate you will see the MSE screensaver and the screensaver starts the above mentioned tasks.