Facebook has said that a "server configuration change" was to blame for the worst outage in its history. Facebook and its apps Instagram, Facebook Messenger and WhatsApp suffered outages for a considerable time on Thursday, affecting users for some 12 hours in most areas of the world, with the biggest impact in North America and Europe, according to the tracking website downdetector.com.

Facebook has only just offered an explanation for the problems it has experienced over the past 24 hours.

The company hasn't elaborated on what the server configuration change exactly meant nor has it said how many users were affected or why the outage took so long to fix. In a tweet, Facebook just apologised and thanked people for their patience. It said it had "triggered a cascading series of issues" for its platforms, including WhatsApp and Instagram.

"Yesterday, as a result of a server configuration change, many people had trouble accessing our apps and services," a Facebook tweet said. "We've now resolved the issues and our systems are recovering. We're very sorry for the inconvenience and appreciate everyone's patience."

The outage was believed to be the worst ever for the internet giant that reaches an estimated 2.7 billion people with its core social network, Instagram and messaging applications. It took the social network giant a full day from when the problems began to offer any explanation. It added that everything was now back to normal.

The outage brought fresh attention to the embattled social networking leader. It is yet another publicity problem for a company already dealing with privacy issues and regulatory probes.

The disruption isn’t likely to hurt advertisers much since they usually pay for ads per click or impression. But they lose potential customers who might have seen their ads when the site and apps were down. Longer term, Facebook’s reputation with advertisers and investors could be damaged, said Wedbush Securities managing director Dan Ives. It didn’t help that it took Facebook so long to explain what was going on, he said. Facebook said on Wednesday that the problem was not related to a “distributed denial of service” or DDoS attack, a type of attack that hackers use to interrupt service to a site, but didn’t provide any other details until Thursday. “In these situations, a lack of transparency is not a good look,” Ives said. “The longer something like this lasts, the more questions there are.”