Box flashes on screen

I was wondering if anyone could assist. Every 2 or 3 hours on my pc, the outline of a black box flashes up on my screen for a fraction of a second. I have cyberghost installed and thought it may be that, but I closed it down, and the box flashed shortly after, so I think it isn't that. It looks like a command prompt box, but it's so quick it's hard to tell. Is there anyway to tell what it is and what's doing it? I want to know what's doing this, as it's a recent development and I'm curious.

I'm having a similar issue.
When i'm in a game, full screen...the displays go black for 3 seconds...then the game is in Windowed Mode.
If i'm not in a game, I see the outline of a Windows "window" for a split second.
I cannot make out anything in the title bar to know what it is. The contents of the window appear black, with the window itself having a white border.
It is happening at hourly intervals...at exactly 43 minutes after the hour, for every hour my computer is on.

It has happened while watching movies, or while the computer is idle as well.

I'm running Windows 10 Home.

I've not updated any drivers or software recently except CCleaner...which I turned the auto-features off for, but it made no difference. The problem started a week ago, and CCleaner has been installed for 3 weeks. So I doubt this is it.

I've been in Event Viewer in Win10 looking for a sign of something occurring 43 minutes after the hour...but there's nothing there. Meaning...?...that whatever it is...is not seen by the os as an "error"?

Windows Defender is my only other security program.
I was going to run MalwareBytes free version to see if it finds anything.
I've looked on the Internet for similar issues and they exist going back many years, but the tendency is for them to all be different applications causing it.
So the next thing i'm looking for is some way to search my system for something that is regularly doing something 43 minutes after the hour. (although I will take a movie of it happening later today...to see if a frame can catch the window and I can perhaps see a name in the title bar)

Any ideas?

Not a clue. I'm WIn 10 Home too, I got creators update a couple weeks ago, coincidence? Using Kaspersky, not WD.

There's another post here about this abibee...have a look, there's some helpful info there:
Quick Window Flashing / Popping Up Periodically - Windows 10 Forums

Just adding, I've also recently had this happening - it kicks me out of games and anything full screen. You might be onto something with the 43 minutes, mine was pretty close to this time too. Will have to see if it happens again in the hour.

I'm thinking it might be nVidia related, not sure if it happened at the same time I installed the new driver and/or GeForce Experience software?

Otherwise, nothing showing in event viewer....other apps I'm keeping an eye on is Steam.

Seems we're not alone, the same problem has also just been reported, and a solution found.

Unknown window appear every so often. Solved - Windows 10 Forums

abibee said:

Seems we're not alone, the same problem has also just been reported, and a solution found.
Unknown window appear every so often. Solved - Windows 10 Forums

Thanks Abibi.

Before seeing the above link...I used a pocket camera to video the window flashing...brought it in to a video editor and saved the frame...I could barely read it, but it was obvious it was related to Microsoft Office. I uninstalled it, restarted the computer and ran CCleaner, restarted and ran CCleaner once more before all the Office registry entries were gone.
The window did not reappear at 43 minutes after the hour again.

I get Office through my employer program called Microsoft Office Home Use Program. It's an online download and if like me you switch to a new computer and don't write down the serial key...you can't register it. I don't use it much at home so left it installed for the past 8 months...waiting for my annual opportunity to buy it again from work.

So...perhaps I could have avoiding uninstalling it...but I don't really need it anyways so no problem.

Yes, it's the Office Background Task runner, I figured it out by enabling process auditing in local security policy. Then, when it flashed, I immediately checked my event log.

Nobody is really sure what this task does, or if it's needed for anything. So disabling it, as suggested in other posts may not be the best solution. If @Jeff1961 's solution works, that might be a better choice.

I use Win 8 and it only just started happening after all this time. I noticed immediately after that another box flashed very fast but I did read the word 'update'. I also use 2007 version of Office so I doubt it is that.