A Three Mobile handset fraud investigation has identified tens of thousands more customers have been hit than was previously thought.
The mobile operator said today 76,373 more customers had been hit than previously thought, a 57 per cent increase on initial estimates made last year.
A spokesperson for Three said while it is not known how long the ongoing investigation will take, it does not expected any more customers to be affected.
In November, Three unearthed criminal activity on a system used to upgrade customers to new devices. Despite reports that up to two-thirds of its 9m customer base had been hit, Three said the data of only 133,827 people had been accessed.
"We have continued to work closely with law enforcement to support the ongoing investigation. During the course of the investigation, additional files were recovered as part of the same activity which we have analysed," Three said in a statement today.
The CK Hutchison-backed firm reiterated that no fraudulent activity had taken place specifically on customer accounts. It said customers wanting to break their contracts would be dealt with on a case by case basis.
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However, personal data such as names, addresses, dates of birth and method of payment had been accessed and could be used elsewhere.
Bank details and passwords were not obtained, Three said, adding it had contacted the latest round of customers affected.
"We ask customers to be cautious about anyone contacting them… We advise caution when dealing with other service providers you may use.
"As always, customers should never give out any banking information," Three said.