Books say that as long as they have hun, frost can`t kill them.
that's true. my winters are pretty cold and my bees do fine if they have plenty of food in. i also put dry, granulated sugar on the inner cover for winter. that way i know they have a little extra if they need it and i only have to pop the outer cover to check it.
they also do well if the hives are covered with snow as long as entrance is not blocked and there is some ventilation. snow insulates the hives. it's the constant rain that's bad here.