The OneNote team just updated the OneNote for Windows Store app, and now, just like OneNote for Windows, you can password protect sections of your notebooks for added security. The full on Windows version has had this capability for quite some time, but now you can easily password protect sections, and they'll be locked to unauthorized users, including page thumbnails:
After unlocking a password protected section, you can view and edit its contents just like any other section—but to protect your privacy, page thumbnails are not shown. Plus, the section automatically locks if you don’t use OneNote for a few minutes. You can also lock all of your password protected sections manually—simply right-click or tap twice on any section tab, then select or tap the Lock Protected Sections button (power users can press Ctrl-Alt-L on the keyboard).
You can get OneNote for Windows Store from our download link, below.