Ah, well - we do say, in the user's guide, that if you don't have enough space to actually store the image, things can fail catastrophically. This is an example. (If the OS doesn't tell us there's an error writing, we don't know - and while you'd expect it to in this case, well, clearly not.
)
Yes, antivirus regularly "catches" things. But that's why I said a "modicum of caution". If you feel it offers you value, though, by all means continue! Personally, I've never found them very useful.