Facebook on Thursday restored service to its main app and Instagram, after the world’s largest social network suffered a major outage that lasted more than 24 hours.

The company also said it was considering whether to refund advertisers for lost exposure due to the problems, which internet outage trackers showed affected users in Europe, Japan, North and South America.

“Yesterday, a server configuration issue made it difficult for people to access our apps and services. We are 100 percent back up and running and apologize for any inconvenience,” a Facebook said.

It is not known whether the server configuration change was a routine task or in response to something specific. The social media platform tweeted that the outage was not related to a DDoS attack.

“We are still investigating the overall impact of this issue, including the possibility of refunds for advertisers.”

Facebook takes tens of millions of dollars of advertising revenue every day.

Meanwhile, the New York Times reported on Wednesday that U.S. federal prosecutors were conducting a criminal investigation into data deals Facebook struck with more than 150 technology companies such as Amazon.com and Apple.

Facebook is also facing lawsuits and regulatory inquiries over its privacy practices, including ongoing investigations by the U.S. Federal Trade Commission, the Securities and Exchange Commission and two state agencies in New York.