Old Mutual has revealed it recently suffered a data breach compromising the personal information and investment values of some customers. The Anglo-South African financial services firm said it detected "unauthorized entry" into one of its systems which led to some customers' personal data being accessed.

A "relatively small" group of customers in South Africa were affected by the breach, the firm said. Customers' personal information including their names, telephone numbers and some investment values were accessed by hackers in the attack.

Old Mutual said no credit card information, banking information, transactional details, medical information or passwords were compromised in the breach.

"We moved swiftly to close access to the targeted system", the company said. "Our control processes kicked in to safeguard customer portfolios and we can confirm that no customers incurred any financial loss.

"We would like to sincerely apologize for any concern this may raise with our customers. We view this case in a very serious light – one customer is one too many. We assure you we are conducting stringent reviews to ensure that no incident of this nature is repeated."

The firm said "immediate steps" were taken to bolster its security and said its systems and surveillance are on high alert. The company is currently notifying all effected customers directly as a precautionary measure.

"Old Mutual has a strong 172-year reputation to uphold," the company said. "We are working tirelessly to deal with this matter effectively and fully restore customers' peace of mind."

The company did not reveal how many clients were affected in the breach, when it occurred or name any suspected perpetrators behind the cyberattack. However, it noted that the breach was not related to the recent devastating Wannacry ransomware cyberattack that crippled scores of companies across the globe.

Old Mutual said it has notified regulators and is working closely with the South African Police Service in an ongoing-investigation into the attack.

"Following the completion of an intensive internal investigation to fully understand the cause, Old Mutual will take the necessary management actions," the company said. "We have ring-fenced the affected accounts and put additional verification and validation processes in place to monitor and safeguard transactions on these portfolios."

IBTimes UK has reached out to Old Mutual for further comment.

The company has warned customers to be wary of any unsolicited phone calls, messages or emails regarding financial offerings, investment offers or inquiries about personal information.