It got me paranoid when I notice the blink-and-you-miss opening and closing of a popup ever so often when using Windows 10. After turning on process audit I finally managed to track it down to officebackgroundtaskhandler.exe. Turns out it is due to Ms Office doing some who-knows-what background handling. Follow the article below to disable the annoying popup.
If you run Microsoft Windows 10, you may have noticed a popup window being launched on the screen once a day, or even regularly.
Source: What is that popup on Windows 10 that disappears after a split second? – gHacks Tech News