Let's say such a virus exist. The better targets would be living humans since their body would be in better shape. As for the brain, the main problem would be memory at least for basic things like body movement. In this case, a living human would be the best. The other thing is that even if a human is affected by a virus that drastically affect the way he behave, the body itself would still need to eat and function as a living human does unless magic is there to help. Muscles need energy, not much any other way around, so eating is a must. In the end, virus affected zombies would be pretty much a human that would act differently than other humans. Apart from this, they would be pretty similar. Maybe the virus could improve/lessen some aspects, but it could not change it THAT much unless the virus manages to change the human body into a totally new species.
The most dangerous aspect of these zombies would be the fact that they are contagious. If you take a virus like Ebola for example, make it less dangerous for the human body (or let's say that it would take months to start being dangerous for the body) BUT that it would start being contagious very fast, this would be crazy. Even crazier if it changed the way humans behave in order to spread faster, but in fact, probably that it would be even more dangerous if the virus shown no sign until a very long time. Just less zombie like.