This is a tale of spies, a $500m cyber arms heist, accusations of an attempt to manipulate a US presidential election and an increasingly menacing digital war being waged between Russia and the west.

It begins with a clandestine online group known as The Shadow Brokers. There is no evidence that it existed before last Saturday, when a Twitter account in its name tweeted at a handful of leading global news organisations with an unusual announcement: it was conducting a $500m auction of cyber weapons.

In a show of faith, the group put a selection of its wares — a 4,000-file, 250MB trove — on public display. Security analysts have been racing to go through the list but it is already clear that at least some of what has been revealed so far is real.