Cursed black box following cursor, on multiple Macs
I have yosemite, and i found a setting that does what you're describing but does not look quite like yours, for me it creates a box AROUND the mouse.
So hopefully you dont have yosemite and thats why. Anyways you can find the setting in:

System preferences -&gt; Accesibility -&gt; Zoom -&gt; More Options


Then when you're here you should uncheck 'Show preview rectangle when zoomed out'. If its not checked, check and uncheck it for good measure.
Found here