Officials in the Brazilian town of Recife, home to one of the most dangerous places to swim in the world, are ramping up shark attack warnings for football fans heading there for the 2014 World Cup / Albert Kok/ Wikimedia Commons

Sharks are known to like gnawing on fibre optic lines but no-one knows why

Google is reinforcing its underwater internet cables to protect them against shark attacks.

The fibre optic lines under the Pacific are being wrapped in a super-hard material similar to Kevlar, which is used to make bullet-proof vests and military armour.

Dan Belcher, a product manager for the company, told the Google Cloud Roadshow the internet giant goes to great lengths to protect its infrastructure, Network World reported.

Sharks appear to have developed an inexplicable taste for underwater cables dating back to the 1980s.

A New York Times report in 1987 said the then new fibre optic cables linking the US, Europe and Japan were being gnawed by sharks, causing phone and computer failures around the world.

In 1985, shark teeth were reportedly found embedded in an experimental line in the sea off the Canary Islands.

One theory is that curious sharks are attracted to the electric and magnetic fields around the cables, which are far stronger than with older copper lines, and mistake it for distressed fish.

Fibre optic cables are able to transmit information much faster than metal and Google is upgrading much of its US network in an attempt to reach internet speeds of one gigabit per second.