South Korea's most popular social media app, used by about 90% of the country's population, is having a very bad week, and one of its CEOs just resigned

• The co-CEO of South Korea's most popular messaging and social-media app Kakao resigned on Wednesday.
• On Saturday, a fire at a data center that houses Kakao's servers locked millions of users out of the app.

Kakao is South Korea's most ubiquitous messaging and social media app, and it's having a very bad week.

On Saturday, a fire was discovered at a data center that houses Kakao's servers, the company disclosed in a regulatory filing. The fire cut off power to 32,000 servers, or about 30% of Kakao's total servers, and led to widespread outages across the app's services, which include payment, banking, and gaming. The data center, located in the South Korean city of Pan-gyo, is operated by IT-services company SK C&C.

CNBC reported that all 53 million of Kakao users were unable to use the app. Tens of millions of Kakao users were unable to withdraw money, buy groceries on e-commerce platforms, call taxis, or send messages to family and friends for more than 24 hours after the fire, Nikkei Asia reported. Insider was not able to independently verify these numbers.

The disruption to the app was so severe that South Korean President Yoon Suk-yeol called for swift measures to resume services, Reuters reported on Sunday. The company issued an apology over the outage.

"We apologize for causing huge inconvenience for such an extended time, due to our preparation and reaction to rectify the situation fell short of user expectations," the company's co-CEO, Namkoong Whon, said in a news briefing on Wednesday, Bloomberg reported.

Then, on Wednesday, Namkoong resigned from his role as co-CEO, effective immediately. His co-CEO, Hong Euntaek, will become the sole CEO of the company.

Following the outage, questions have been raised about the public reliance of the app.

"If the market is distorted in a monopoly or severe oligopoly, to the extent where it serves a similar function as national infrastructure, the government should take necessary measures for the sake of the people," Yoon said, per the BBC.

Yoon also ordered an investigation into the causes behind the incident, stating that the services were "like a fundamental national telecommunications network as far as the public is concerned," per Reuters.

As of Wednesday, most of Kakao's systems were restored, but some functions remain shaky.

The company's messaging app, KakaoTalk, has 47 million active accounts in South Korea, Reuters reported, citing a company report released in August. South Korea's population was around 51.8 million people in 2021, which means over 90% of its citizens have a Kakao account.

Kakao did not respond to Insider's request for comment.