Stretching between London and Frankfurt, there is a private, mysterious network that is twice as fast as the normal Internet. The connection, provided by a series of microwave dishes on masts, was once completely secret: only one very rich company was allowed to use it, and no one else knew about it.

A couple of years later though, a competitor completed its own microwave link between the two cities—and thus the first company, not wanting to lose out on potential business, revealed that it too had a link between the cities. If a competitor had never emerged, that first link would probably still be shrouded in secrecy today.

Similar stories can be found all over the world, but because these networks are privately owned, and because they’re often used by financial groups trying to find an edge on the stock market and eke out a few extra billions, you have to dig deep to find them.