According to the paper, the reporter was sold information on thousands of accounts for £4.25 ($8) each. The details included passwords, addresses, phone numbers, credit card, driving license and passport information.
A spokeswoman for the City of London told PA that an investigation was underway and "therefore it would be inappropriate for us to provide further details at this stage." She added all the financial institutions identified have been fully informed of the situation.
Experts said in countries such as India, controls were not yet in place to prevent this kind of incident happening.
"In the U.K. we have a set of high standards for banking. This attitude of business does not exist in India yet," said Paul Howard, managing director of data security company Disuk. "It is very easy to bribe someone when their view of what is a lot of money is different to yours."
Donal Casey, Consultant, Diagonal Security said banks and the call center companies should have security processes and procedures in place that alert them to this type of fraudulent or suspicious behavior.
"Something clearly has gone wrong in this instance. The banks and the outsourcers must quickly review their security practices, to identify how this could have possibly happened. It shouldn't be possible for one individual to collect this level of detail on thousands of customers," said Casey.
Howard said there was a lack of separation between different departments in these outsourced operations and this could lead to one department holding all the details on account holders. He urged banks to ensure that outsourced companies separate information in order to keep a good level of security.
As reported in SC Magazine earlier this week, the huge security breach that exposed more than 40 million credit cards to potential fraud appears to be the work of organized criminals, according to experts.