In our age of wireless technology, it might be hard to believe that we’re all connected by a few hundred cables running along the sea bed. From the memes we send to friends, to the intelligence used by the military, virtually all internet data between the continents travels along wires thinner than a human hair. If they sound vulnerable, it’s because they are. On average a hundred are accidentally severed each year. And security experts are warning they could be a target for military or terrorist sabotage.

Caitríona Perry speaks to Nicole Starosielski, professor at the University of California, Berkeley and author of The Undersea Network, who guides us through these secretive networks. And our security correspondent Frank Gardener helps us understand how vulnerable they are.

Producers: Richard Moran and Alix Pickles

Sound engineers: Mike Regaard and Hannah Montgomery

Assistant editor: Sergi Forcada Freixas

Senior news editor: Sara Wadeson