Alex Gibney's "Zero Days" is a documentary thriller about warfare in a world without rules- the world of cyberwar. The film tells the story of Stuxnet, self-replicating computer malware (known as a "worm" for its ability to burrow from computer to computer on its own) that the U.S. and Israel unleashed to destroy a key part of an Iranian nuclear facility, and which ultimately spread beyond its intended target. It's the most comprehensive accounting to date of how a clandestine mission hatched by two allies with clashing agendas opened forever the Pandora's Box of cyberwarfare.