cyberattack
A magnifying glass is held in front of a computer screen in this picture illustration taken in Berlin, May 21, 2013. Reuters/Pawel Kopczynski

Update as of 4:23 a.m. EST: In a response to Lizard Squad’s claim that it was responsible for the worldwide outages of several social media sites on Tuesday, Facebook, which was one of the affected services, denied that it was hacked by the group. According to the company, its own engineers had caused the anomaly.

“Earlier this evening many people had trouble accessing Facebook and Instagram,” a Facebook spokeswoman told BBC News. “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.”

Lizard Squad, a group of hackers sympathetic to the Islamic State group, claimed responsibility for the worldwide outage of several social networking sites on Tuesday. The websites of Facebook and Instagram were down for about 40 minutes.

Lizard Squad, which claimed to have hacked the website of Malaysia Airlines on Monday, posted on Twitter that it had also targeted other social networking services, including Tinder, AIM and Hipchat on Tuesday. Another tweet from the group said: “If only we didn't use twitter to communicate...”

Facebook, Instagram and other affected services were back online though Facebook's site was responding slowly, according to some users.

It was not clear what caused the outages -- which first occurred around 1:00 a.m. EST -- on both social networking websites. While Facebook said, following the outage, that it was working on a fix, Instagram said on its Twitter account -- the tweet is no longer visible -- that it was aware of an outage and was working to resolve the issue.

The Lizard Squad, which had previously taken credit for denial-of-service attacks on Xbox Live and Sony Playstation Network, launched a cyberattack on Malaysia Airlines’ website Monday and posted an image of the group’s logo on the website’s main page, along with the message: “Hacked by LIZARD SQUAD - OFFICIAL CYBER CALIPHATE.”

On Tuesday, the hacker group also threatened to launch more attacks on the Malaysia Airlines website.

During Tuesday’s outages, users of both Facebook and Instagram took to Twitter to express their concerns, making #Facebookdown one of the top worldwide trending topics. Here are a few reactions on Twitter: