Can You Identify this Montana Critter?

You've probably seen more animals than you care to count in Montana, but have you ever seen one of these?

Yesterday, I was carrying firewood into my house after work when I saw an animal I'd never seen before running across the horse pasture in front of my house. Living in Bear Canyon, I've seen all kinds of animals, but I've never seen an animal quite like this.

It almost looked like an albino ferret. It was completely white and a little over a foot long. Have you ever seen one of these?

Do you know what kind of animal it is?