That is a daring aka bold jumping spider, Phidippus audax (Araneae: Salticidae).
This is an extremely common spider. It is not a dangerous spider and should not be cause for alarm. Bold jumping spiders are usually found running about over the bark of trees and under stones and boards, on window screens, and other such places. This spider passes the winter in the immature stage in groups or "hibernating aggregations." Common overwintering sites include inside hollow logs, under tree bark, and inside buildings in enclosed, protected sites.
Jumping spiders have the keenest vision of all spiders that they use to hunt their prey in board daylight. Jumping spiders do not build snares or webs to catch their prey. They stalk their prey much in the same way as a cat does with a slow and deliberate approach, and then a sudden, quick jump. Just before jumping, the spider extends its front legs (for seizing the prey) and spins a line of strong silk to act as an anchor. While no snare is built, all jumping spiders spin closely woven retreats for molting, hibernating and spending the night. These retreats are commonly located under bark, between stones and in rolled leaves.