I can't remember what this movie is called?

In the beginning there is a woman trapped in a room with a window and
shes tied down.Then you see a guy outside when a zombie virus breaks
out and zombies are attacking the building. There are gunners up above
shooting the zombies. The woman trapped in the room sees a zombie
outside the window that keeps running into the glass. I don't know if
this is completely accurate but its all I can remember.
I think it also had a part where one of the gunners helped them escape
the area I think the gunner later helped them escape by pushing the
car away in some kind of fog or something.