A Twitter account that purports to speak for hacker group "Lizard Squad" posted messages suggesting that it was behind an attack the temporarily blocked several major web sites.
Facebook, its photo-sharing site Instagram, and other popular social networking sites, were unavailable from around 0600 GMT for upward of an hour according to user reports and Web monitoring sites in countries across the Americas, Asia and Europe.

Earlier on Monday, the website of Malaysia Airlines was commandeered for several hours by hackers who referenced the Islamic State jihadists and threatened to expose data taken from the carrier's servers.

The attack, whose motivation remained unclear, was claimed by the "Lizard Squad", a group that has taken credit previously for denial-of-service attacks around the world.
It was not clear why the troubled airline was targeted, but the Lizard Squad said on its Twitter feed that it was "Going to dump some loot found on malaysiaairlines.com servers soon."
Visitors to the website were re-directed to another page bearing an image of a tuxedo-wearing lizard and reading "Hacked by LIZARD SQUAD - OFFICIAL CYBER CALIPHATE".
It also carried the headline "404 - Plane Not Found", an apparent reference to the airlines' puzzling loss of flight MH370 last year with 239 people aboard which tipped the already struggling carrier into crisis.
Media reports said versions of the website takeover in some regions included the wording "ISIS will prevail".