Answer:
To be breif, yes. But only when provoked. Otherwise, they would rather be left alone.
I'd like to add to this... Many researchers who go out and follow wolf packs have in fact proven wolves, as said above, do not act vicious unless provoked. I have seen videos of some researchers who go right up to the pack, sit down, and the wolves come over and begin licking the researchers face.
Wolves are family oriented, and are rather calm by nature. The best way to make a wolf attack is to act in a threatening manner toward that wolf, go near their pups, or to approach a lone wolf that has no pack and might attack in fear of dying otherwise.
We have a opinion on wolves being 'vicious' because they used to attack farm animals. Well, all wild animals will attack farm animals if they need food. However, it is rare to hear about a wolf attacking a human at random... More attacks come from wolf-dogs, which are a mix breed of a dog with wolf genetics. People thinking mixing the breed will calm the beast. Truth is, that creates the beast. Wolf-dogs are more aggressive and likely to kill than a normal wolf. Go figure, right?
In short, they are vicious if you provoke them or you are the animal they are hunting...but in reality, no, they are not 'vicious'.