[Updated on January 27 at 11am]
Users in Hong Kong, the rest of Asia, Australia and the US were left wondering what happened when they were unable to access their accounts for around an hour yesterday.
Instagram, which was acquired by Facebook in 2012, was also down.
Netizens reacted on Twitter, and soon #facebookdown #instagramdown and #ThingsIDidWhenFacebookWasDown were trending topics. Jonathan Lopez, from Canada, summed it up for students: "That awkward moment when Facebook crashes so you're forced to do homework."
Other jokers tweeted about how they took photos of their food around to friends and waited for a thumbs-up. Others found that "poking" random strangers was not a good thing to do IRL (in real life).
It wasn't long before people sought someone to blame, with the first suspect being North Korea. But then a shadowy hacker group Lizard Squad took credit for the attack on Twitter. The group has been linked to other high-profile hacks, including Monday's attack on the Malaysian Airlines site.
Lizard Squad is best known for 2014 attacks on the PlayStation and Xbox gaming services, as well as its claims to have taken down North Korea's internet on December 22.
In Monday's attack around 10am, reports Bloomberg, visitors to the Malaysia Airlines website were greeted with an image of an Air Malaysia plane, and the message: "404 - Plane Not Found." The reference to the still missing Flight MH370 was signed "Cyber Caliphate" and accompanied by a hip-hop tune; the tab marking the site was changed from "Malaysia Airlines" to "ISIS Will Prevail". Bloomberg says it is certain IS had nothing to do with the attack even though the Malaysia Airlines' home page changed again, to a picture of a lizard wearing a monocle and a top hat, with the message: "HACKED BY LIZARD SQUAD - OFFICIAL CYBER CALIPHATE."
Facebook has denied it was hacked, saying the glitch was caused by an internal error.