This applies from all versions of Windows 8 to Windows 10.

This only occurs if you have a touchscreen PC and have ever used the handwriting-to-text function. It is stored in a file called 'WaitList.dat' and is located on your computer at:

Once you start using the handwriting feature, it turns the 'TextHarvester' feature on. Windows then performs a search index of your entire computer (usually used for making subsequent searches faster). The 'TextHarvester' is supposed to improve the accuracy of the handwriting-to-text function, but in so doing it also stores the text from all your emails and documents found on your PC.
So if you made a note about your bank details, or a word document containing a list of passwords for various websites, those details will all be recorded in the file WaitList.dat Even if you decide to then move the documents off your PC, the sensitive information still remains inside WaitList.dat.
A hacker or any malware could easily then read the WaitList.dat and search for passwords and logins to all sensitive information.

The easy way around this is to either not use the handwriting-to-text function, delete WaitList.dat (but remember it will be recreated), and turn the Windows Indexing feature off for a specific drive.
1. Go to 'My Computer' or 'Computer' and right-click on your drive (C, D, etc) and choose Properties.
2. On the General tab, untick the checkbox at the bottom called "Allow files on this drive to have contents indexed in addition to file properties"
3. A popup dialog will appear. Select 'apply these settings to all files and subfolders'.

To turn the Windows Indexing feature off for ALL drives: 1. Go to Control Panel and click on Administrative Tools.
2. Click on Services
3. Scroll until you find either "Indexing Service" or "Windows Search" in the list. You'll see it's either in the Started state and is set to Automatic.
4. Double-click on "Windows Search" and click the Stop button to stop the service. Then change the Startup Type to "Disabled".
5. Restart

Searches will take longer, but at least the index in WaitList.dat won't be recreated. Remember to delete WaitList.dat as mentioned above!