Facebook said on Friday that users around the world had once again struggled to access its services for hours due to an adjustment to its system, just days after a similarly caused massive outage.

“Sincere apologies to all those who have not been able to access our products in the past two hours,” a Facebook spokesperson told AFP at around 9:30 p.m. GMT.

“We fixed the problem, and everything should be back to normal now.”

DownDetector Website Issue Tracker show spikes in reports of problems accessing or using Facebook and its photo-centric Instagram network, as well as Messenger and WhatsApp, starting about three hours earlier.

Facebook attributed the problem to a configuration change on its computing platform and said it affected social network and Instagram, Messenger and Workplace users around the world.

People have flocked to Twitter to express their frustration.

“What’s going on with Instagram? Read a tweet that included a photo of cartoon character Bart Simpson sitting in a corner in apparent punishment.

“It’s not even 4 days and it’s already gone down.”

“Problems with Instagram, Facebook, Facebook Messenger and WhatsApp AGAIN!” read a complaint in a DownDetector discussion board.

Hundreds of millions of people were unable to access Facebook, Instagram or WhatsApp for more than six hours on Monday, underscoring the world’s dependence on platforms owned by the Silicon Valley giant.

In an apology blog post, Santosh Janardhan, vice president of infrastructure for Facebook, said that day’s outage was caused by “configuration changes” on the routers that coordinate network traffic between data centers.

Cyber ​​experts believe this problem boiled down to something called BGP, or Border Gateway Protocol, the system the Internet uses to choose the fastest route to move packets of information.

Sami Slim of data center company Telehouse compared BGP to “the Internet equivalent of air traffic control.”

In the same way that air traffic controllers sometimes change flight schedules, “Facebook has updated these routes,” Slim said.

But this update contained a critical error.

It is not yet clear how or why, but Facebook’s routers essentially sent a message to the internet announcing that the company’s servers no longer existed.

Friday’s blackout was unrelated to the one at the start of the week, according to Facebook.

Experts say Facebook’s technical infrastructure is unusually dependent on its own systems.

Social media outages are not uncommon: Instagram alone has seen more than 80 in the past year in the United States, according to website builder ToolTester.

Facebook services are crucial for many businesses around the world, and Facebook accounts are also commonly used to log into other websites.

Facebook’s apps are used by billions of people every month, which means blackouts can affect a large part of the world’s population.