I think that we would have a different definition. A lap dog could nip at you in an unprovoked attack. Annoying but not threatening, so in my book, not a vicious attack. I see a vicious attack as having a more serious outcome. I see vicious as a serious, determined attack that is not easily broken off, even by the dog's handler.
Unprovoked is difficult to judge. The person may have no idea why the dog attacked but to the dog, there was a triggering event that was clear to it. Remember yesterday on FR, there was a pit bull attack that was allegedly triggered because the guy's girlfriend had her teeth whitened and she smiled at the dog who took the smile as a threatening growl and attacked. She had no idea this would trigger the dog who savagely mauled her and torn off her nose.
Pitbulls are a whole different topic. I’ll never own one. I do like some protective breeds though. I can handle the Belgians, shepherds, coons, mastiffs easily enough. Need a strong alpha presence and be able to read body language.
These dogs clearly had a terrible owner who just wanted to be tough and let the dogs do whatever.