Vodafone believes its customer database was compromised from an employee or dealer sharing the access password, giving the recipient access to the personal details of millions of customers, ABC News in Australia reports.

'It appears to have been a one-off incident, but we are investigating that thoroughly now and we will have a much better picture of that in the next 24 to 48 hours,' said Nigel Dews, Vodafone's chief executive. 'We did take this data security issue very seriously. It's very important that we uphold the highest standards of data integrity for our customers.'

Dews went on say that passwords are being reset every 24 hours to make sure his company's customer records are kept safe until the investigation concludes.

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