This object was 3 feet long, absolutely harmless. But something the size of a house, if it impacted, could be very destructive. And that is quite possible without being detected.
Someone has mentioned the Oort cloud, but that's where the long-period comets hang out. Some other person reckons that something is affecting the asteroid belt. However, asteroids often follow comets and sometimes comets fragment and end up as space debris. Some even think that this is what happened to Elenin and maybe we're getting chunks of it raining down here & there.