It's remarkable how Gibney packs complex, jargon-heavy ideas into a neat package.

Be very afraid.

This documentary might be better titled Day Zero, because it features a doomsday scenario in which cyberwarfare shuts down the electricity grids and other networks of entire countries, using computer malware.

A shocking look at the future of international warfare, Zero Days is at its best when embroiled in computing language and incident breakdowns, and at its worst almost never.