To make sure that these file stay secure when you're offline, you can encrypt the file stored on your local computer. So just in case your computer is lost or stolen the data won't be compromised.
To enable offline file encryption:
- From the Start menu select Control Panel (in the Classic View).
- Double-click the 'Offline Files' applet.
- Click the Encryption tab.
- Press the Encrypt button.
- Press the OK button.