Black Box Surrounding Cursor - HELP

Please help - this is driving me insane!

So I upgraded to macOS High Sierra. No problems. Then I log in, and there's this annoying black box around my cursor and following it everywhere I go. In the screenshot I've attached, it's the black box around the google logo.

I cannot figure out how to get rid of this, but it's annoying the living daylights out of me. Please help.