Transparent magnifier just popped up

This is one I've never heard of before. A transparent window about 2x3" just opened that magnifies everything it's over. The cursor is in the middle of the window and it moves wherever I move the cursor to. So far I haven't found any way to get rid of it, although I haven't tried rebooting yet. Anyone ever have this happen before? What's the remedy?

The specs for my system are in my signature, below.

 

I was so frustrated by that Magnifier that this morning I did a reboot before I saw your replies. The reboot fixed the problem. I still don't know why the dopey thing popped up in the first place. I've never programmed any hot keys, and I think I was just using the mouse when the thing first appeared. But thanks for your replies. At least now I have an idea of how to go about getting rid of the Magnifier if I ever hit the magic combination again.