Facebook and Instagram have denied they were hacked after their services were down for 40 minutes on Tuesday morning, with millions of users unable to access their accounts from around 6.10am GMT.
This outage is the longest Facebook has experienced since September 2010, when services were unavailable for two hours.
Facebook says that the problems were caused by an internal issue and not an external attack, and that no information was compromised.
Users attempting to gain access to the social media site were met with the below error message.
Rival social media website Twitter remained in use during the outage, with users taking to the site to voice their thoughts.
A spokesperson for Facebook, which also owns Instagram, released a statement saying:
Earlier today many people had trouble accessing Facebook and Instagram. This was not the result of a third party attack but instead occurred after we introduced a change that affected our configuration systems.
We moved quickly to fix the problem, and both services are back to 100% for everyone.
A hacker group named Lizard Squad have hinted they were responsible for the 40 minute outage on their Twitter account, as well as linking themselves to other sites that went down including Tinder, a dating app that works through Facebook, and Myspace.
However, some security experts have expressed doubt that Lizard Squad would have been able to hack into Facebook, suggesting that they were not actually involved and aimed to increase their profile through association with the outage.
Mark James, a security specialist at anti-virus firm ESET, did not think it was likely:
As great as the prize would be I doubt Lizard Squad or any of the other mainstream teams would be able to take down Facebook directly. A few have tried and stated that they will but I think it’s highly unlikely they will succeed.
It’s interesting to see Lizard Squad taking the glory for this one, association is a powerful tool and being talked about at the same time as these two giants going down will achieve the same thing to a small degree.
Adam Winn, product manager for software firm OPSWAT, also expressed his doubt:
The outage was global and simultaneous, meaning, only the most well-crafted DDoS would shut down all these affected services, all across the globe, at the same instant. That type of monumental effort would have come with much louder bragging by Lizard Squad.
Lizard Squad have previously claimed to be responsible for other high profile hacks.
They linked themselves to the Sony and Microsoft hacks over the Christmas period.
Most recently they claimed the hack of the website of Malaysian Airlines on Monday morning, replacing their homepage with a picture of a lizard in a top hat.
The hacker group then claimed that they would release information on the Malaysian Airlines but did not specify what.
Malaysian Airlines have denied the hack and declared that customers’ personal information was secure.
UPDATE, 17:30 27/1/15:
It appears as though someone with links to Lizard Squad has hacked the Twitter account of celebrity Taylor Swift, as recent tweets from her account suggest. One tweet stated ‘go follow my boy @lizzard’, referring to an account which describes the user as an ‘Original Digital Gangster’ and ‘Leader of Lizard Squad’. The user also seems to link themselves with terrorist organisations in their Twitter description. The tweets on Swift’s account have since been deleted.
Another tweet tells her followers to follow an account under the name of ‘veriuser’, which some people on Twitter have speculated as being the primary hacker responsible. It is assumed they are linked to Lizard Squad due to the references to Twitter user ‘Lizzard’. The ‘veriuser’ Twitter account was suspended almost immediately after the hack.
Swift’s Instagram account also seems to have been hacked, as offensive images and messages saying to follow unknown users are published on her feed. Londonmultimedianews.com has screen-shots of these posts but has decided not to reproduce them as they represent evidence of computer crime and harassment.
These Instagram posts have since been deleted.
Twitter user Lizzard has said they will release private pictures of Swift when they have received bitcoin payment.
Twitter user Lizzard’s account has been suspended.
Taylor Swift has published a post on her blog on the Tumblr website referring to the hack:
My Twitter got hacked but don’t worry, Twitter is deleting the hacker tweets and locking my account until they can figure out how this happened and get me new passwords.
Never a dull moment.
She has also tweeted about the incident in the style of her song Shake It Off, in which she sings ‘Cause the haters gonna hate, hate, hate, hate, hate’, and denied the hackers’ claims of gaining access to private photographs: