Most likely a satellite. I have seen several cross the face of the moon while using a video camera and none of them have been exactly square.
Somewhere, I have heard, there is a programme that helps you predict things like thisfor your locatoin - if you follow the Spaceweather page (
www.spaceweather.com) there are sometimes images of the space station passing in front of the sun (which is the same angular size as the moon from our perspective). I'd love to know where you can find this info...(hint hint - someone out there has to know!)