African mobile giant MTN Group announced that a cybersecurity incident has compromised the personal information of some of its subscribers in certain countries.

MTN Group (formerly M-Cell) is Africa’s largest mobile network operator, with a strong Asian market presence. The company has nearly 300 million subscribers across 20 countries and an annual revenue surpassing $11 billion.

The telecom giant noted that its network and billing systems weren’t impacted by the attack, though an investigation to determine the exact scope and impact is ongoing.

“MTN Group would like to inform stakeholders that it has experienced a cybersecurity incident that resulted in unauthorised access to personal information of some MTN customers in certain markets,” reads the announcement.

“Our core network, billing systems, and financial services infrastructure remain secure and fully operational.”

However, MTN says that an ‘unknown third-party’ claims to have accessed data from the company.

Regarding those claims, the telecom firm notes that its investigation hasn’t confirmed a compromise to customer wallets and accounts, so it’s unclear exactly what has been exposed.

MTN says it has informed the South African Police and its country’s relevant regulatory and data protection authorities to support its investigations. Affected customers will also be notified soon.

Meanwhile, MTN advises customers to follow these measures to protect themselves from attacks:

• Place a fraud alert on your credit report via any major credit bureau.
• Keep MTN, MoMo, and banking apps/devices updated.
• Use strong, unique passwords and change them regularly.
• Avoid clicking on suspicious or unexpected messages/links.
• Never share passwords, PINs, or OTPs via phone, text, or email.
• Enable multifactor authentication wherever possible.

At the time of writing, no ransomware actors have claimed responsibility for an attack at MTN.

BleepingComputer has contacted the African telecommunication services provider to ask which markets were impacted, but we are still waiting for a response.