By Eric Auchard
FRANKFURT (Reuters) - Access to Facebook (O:FB), the world's largest social network, and its Instagram photo-sharing site, were blocked around the world for up to an hour on Tuesday, which the company said later was due to an internal fault and not an outside attack.
The outage at Facebook, which started around 0600 GMT, appeared to spill over and temporarily slow or block traffic to other major Internet sites, according to web and mobile user reports from around the globe.
U.S.-based online match-making site Tinder, a unit of IAC/InterActive Corp (O:IACI), and Hipchat, the workplace instant- messaging service of Australian enterprise software company Atlassian, were also down around the same period, but recovered.
A hacker group associated with other recent high-profile attacks on other online services sought to claim responsibility for the outages, but Facebook said the fault was its own.
"This was not the result of a third-party attack but instead occurred after we introduced a change that affected our configuration systems," Facebook said. "Both services are back to 100 percent for everyone."
Users in the United States and many countries in Asia and Europe reported that they were unable to log on to the websites of Facebook, Instagram and corresponding mobile apps including Facebook and Facebook Messenger.
During the outages, Facebook users were greeted with the message: "Sorry, something went wrong. We're working on it and we'll get it fixed as soon as we can."
"If you run a service with the capacity (and complexity) to deliver media for hundreds of millions of users, it's inevitable that things don't always go according to plan," said Steve Santorelli, a former London police detective and now a researcher at U.S. threat intelligence firm Team Cymru.
Facebook counted more than 1.35 billion web and 1.12 mobile phone users on a monthly basis in September, the latest date for which official figures are available.
Earlier on Tuesday a Twitter account that purports to speak for hacker group "Lizard Squad" posted messages suggesting that it was behind an attack that temporarily blocked several major web sites, including Facebook and Instagram.
The Lizard Squad is a group of unknown hackers that has taken credit for several high-profile outages, including the attacks that took down the Sony (T:6758) PlayStation Network and Microsoft's (O:MSFT) Xbox Live network last month.
Santorelli said that attacking Internet sites which operate at the size and scale of Facebook via a classic distributed denial of service attack would be a huge undertaking, which, while not entirely impossible, would be "monumentally hard."
Denial of service attacks direct thousands of infected computers under an attacker's control to ping a site or sites, thereby slowing or blocking access for regular users.
Such attacks can create congestion on branches of the Internet where the site is located, slowing Web traffic and affecting access to unrelated services.
As a precaution, Facebook users are advised to change their passwords and review their privacy settings, Santorelli said.