I speak from experience.

One animal that I was mauled by was a big Chow.
This WAS a friends trusted dog....for around a year.
It knew me and I thought that I knew it.
One day, sitting in the living room watching TV, it calmly walked from the other room up to me. As soon as he got to me, he turned into the Tazmanian Devil.
My friend beat it and apologized. It was the first time he said it ever happened. He mangled my dominant hand.

The next week he did the same thing to his girlfriend's best friend who visited. It mauled har face.
He finally got rid of it. It was given to a farmer where it could run loose. ......and get plenty of exercise.
Hopefully it never came in contact with any people besides the owners

These breeds, if kept, must be treated with the same rules as a wild animal. If they harm someone like the terrier did to that girl, it should be destroyed immediately.