The South African telecommunications company MTN Group said on Thursday it suffered a cyberattack that exposed the personal information of an unknown number of customers. 

The Johannesburg-based firm said an “unknown third-party has claimed to have accessed data linked” to parts of its system and that the incident “resulted in unauthorised access to personal information of some MTN customers in certain markets.”

South African Police Service and the country’s Directorate for Priority Crime Investigation have been informed of the incident while other law enforcement agencies in countries they serve have been notified of the attack. The statement does not say how many customers were impacted but MTN Group said it is in the process of notifying people.  

MTN Group operates in more than 20 countries and has more than 200 million subscribers as one of the largest mobile operators in the world. The company reported about $9 billion in revenue last year, largely due to its widespread prominence in South Africa, Ghana and Nigeria.

“Our core network, billing systems and financial services infrastructure remain secure and fully operational,” the company claimed. “At this stage we do not have any information to suggest that customers’ accounts and wallets have been directly compromised.”

The company did not respond to several questions about how many people were impacted, what kind of data was stolen and who was behind the attack. No cybercriminal operation has claimed the incident as of Friday. 

Nigerian news outlets reported that the cyber incident did not affect operations in the country. 

This is the latest attack on a South African telecommunications company after another major player in the sector, Cell C, confirmed that data was leaked on the dark web following a cyberattack last year.

South Africa continues to deal with near-constant cyberattacks on its major institutions and companies, prompting an array of cybersecurity laws and frameworks designed to address the issue. Last month the country’s largest chicken producer lost more than $1 million due to a recent cyberattack that caused delivery delays and other issues.