Hmmm, I see this thread was moved and I got no notice of it. Anyway, I THINK I found the cause. I run an Oracle Virtualbox WIN10 VM to use as a (LOL) sandbox for questionable items I find in posts on here before I report them as malware or whatever. It seems that is what bit me and I believe I know where/when I got it. Unfortunately (or fortunately) the guy was nuked after I reported his post.
After I reboot, I no longer have the issue but, so far, as soon as I load the VM it returns. That's how it looks at the moment, of course I can easily be proven wrong although I have replicated it about 10x so far. If that is the case it's easy enough to nuke the VM.
So, you had shared clipboard enabled?
If so, this definitely makes sense. If it isn't, nuking the VM does not necessarily mean your problem is solved.
And for the future, you might want to make sure to disable any interfaces such as shared folders, shared clipboard, network interfaces, etc..