Mobile phone provider Three has written to more customers as it continues to investigate fraudulent activity.
The network says it first became aware of criminal activity taking place on its customer upgrade system in November 2016.
Fraudsters obtained access in an attempt to order and then sell on handsets illegally. Three contacted 133,827 affected customers at the time and took steps to block this activity and add further security. A small number had been unlawfully upgraded to a new device by these scammers.
However, during the investigation new information has been obtained which means 76,373 more customers may have had their information compromised. These customers have now been contacted by the network, although no fraudulent activity has yet been identified against this second group.
The provider says no financial information, bank details, passwords or PINs were viewed or obtained as they are not stored on its upgrade system.
Information which is located on the system includes name, address, date of birth, handset type, contract start and end date, upgrade eligibility date, payment type, tariff, billing date and mobile number.
Three says it is continuing to liaise with police agencies and has contacted affected customers by letter and text message.
If customers require further information they are advised to call customer services - 333 from their mobile phone.
A statement says: “We have contacted affected customers to support them. We ask customers to be cautious about anyone contacting them. If it is a call from Three and you are in any doubt that it is genuine, end the call and call us back on 333 from your Three mobile. We advise caution when dealing with other service providers you may use.
“As always, customers should never give out any banking information. If affected customers are concerned, we are also making enhanced Noddle credit check services available at no cost.”