National Australia Bank has been forced into a defensive stance over its treatment of customer data, after a business owner took issue with what she saw as 'Big Brother' style monitoring of her banking relationship.The issue arose after Fairfax Media and the ABC yesterday reported how a dissatisfied NAB customer sounded out ANZ over a car loan, only to be spooked to receive an immediate counter-offer from NAB.The bank initially delayed, before countering with a media release, asserting that "NAB believes in lending responsibly to our business customers. This means we do use a range of information sources, including limited information from credit bureau Veda, to manage relationships with our customers."The NAB media release added that the information from Veda allowed its business bankers to verify that their business customers "are borrowing within their means and ... to understand the intent of the finance and how it will impact on their business operations."NAB insisted that the information received from Veda only relates to business banking customers. "No consumer credit information is provided by Veda to NAB," the bank statement concluded.Veda, recently taken over by US outfit Equifax, refused to elaborate on how information obtained from banks' business customers was used."Banks may use many sources of data to manage their relationships with their customers, some of which may be their own, as well as through a variety of third parties," a Veda spokeswoman told Fairfax.The incident has re-opened debate on how data held by multiple sources should be treated, and how it can be shared in a way that does not compromise - nor appear to compromise -customers' rights to privacy and control of their own data.