We have a house built in the late 60s/early 70s that was clearly renovated (in about 2004) by an idiot who had no concern for safety or building codes or anything else.
We removed a heavy glass chandelier with the intention of putting in a ceiling fan, and found that the box was clearly a plastic one designed for lightweight lighting fixtures and not anything heavy, and furthermore, was not secured to anything but instead was just sort of floating in the celing. In fact, it seemed so flimsy we didn't want to put the chandelier back up.
So we thought fine, we'll just stick in a lightweight fixture for now until we can get a pro out to re-do the box, since we eventually want to replace all the ceiling fixtures anyway.
However, for a few reasons related to how flimsy and badly-installed the box is, we don't think it's really safe to put anything back on it--the holes to screw a mounting strip onto are stripped, for one thing, so they don't really hold securely.
How can we safely cap off the wires (power, neutral, and ground) and put a cover on the hole in the ceiling until we can get an electrician out to look at it and fix it? Obviously we don't want to have live wires there but there's no way we can leave the breaker off indefinitely.
BTW we have aluminum wiring.