What kind of spider is black with two white stripes on its butt, and is found in Montana?

Question

I've had 3 of these spiders in the last week in my house. They are a medium sized spider and the two white lines run parallel and from front to back on the butt.

Answer 1

Lots of spiders here -

http://www.spideridentification.org/

http://www.badspiderbites.com/spider-ide...

http://www.aboutbugsbugsbugs.com/spiders...