Facebook and Instagram have denied their services were hacked today, blaming a 40-minute outage on an internal systems issue.
The sites were unavailable across the world earlier today, with a hacking group appearing to claim responsibility for the outage.
A spokesman for Facebook, which owns Instagram, said: "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."
The technical problems affected some other apps, including online dating service Tinder, which rely on Facebook servers to work.
A hacking group called Lizard Squad, which has previously claimed responsibility for bringing down online services, posted a message on Twitter this morning appearing to link itself to the outage.
It said: "Facebook, Instagram, Tinder, AIM, Hipchat #offline #LizardSquad".
Social media users, who were relieved to still be able to access Twitter, shared their complaints about the outage.
Scarlett Moffat, from the Channel 4 show Gogglebox, tweeted: "What Instagram and Facebook are down!! But how will I know what your morning Starbucks looks like."
Twitter user Vince Caso said: "Livetweeting is my last comfort. It is so difficult to judge people in 140 characters. I miss Facebook."
Fortune Feimster commented: "Facebook and Instagram are back up! Everyone can get out of their foetal position."
Andrew Pope, an engineer at Facebook, posted on to the Facebook Developer's website to alert app creators to the "major outage" which he said lasted up to an hour between around 6.10am and 7.10am.
"Our engineers identified the cause of the outage and recovered the site quickly," he wrote.
"Thank you for your patience.
"We are sorry for any inconvenience this may have caused you and the users of your apps."