Installation Alert

Hey...

I logged into MacBook Pro (OS X Yosemite 10.10.1) after it was asleep for the night. Came back about 1/2 hour later and had "Installation Alert" (iTunes) box on the screen.

I didn't download, update or do anything to initiate this -- Girl Scout's honor.

How do I cancel this installation and get rid of this Alert without installing, since I don't actually trust that it's just installing an update of iTunes, since I didn't initiate it.

Thanks!