Hacker group Rex Mundi has published thousands of loan-applicant details it siphoned off from US payday loan outfit AmeriCash Advance.

The move follows AmeriCash Advance's refusal to sump up $15,000 in what Rex Mundi describes as an idiot tax for maintaining insecure systems and what AmeriCash Advance characterises as an extortionate demand. Rex Mundi said it extracted AmeriCash Advance's customer database on 15 June, via an insecure page designed for affiliates of the finance firm.

"This company which specializes in payday cash advances (basically small loans for low-income workers, which are vastly overpriced) left a confidential page unsecured on their server," Rex Mundi explained. "This page allows its affiliates to see how many loan applicants they recruited and how much money they made. Not only was this page unsecured, it was actually referenced in their robots.txt file (Bad, bad move, guys)."

"We managed to download thousands of loan applicant records. This data contains the names of applicants, the amount they applied for, their email addresses and the last four digits of their SSN. In addition, some 'problematic' applications also include comments left by AmeriCash Advance's employees about the applicant and the name of the applicant's bank. As usual, we will publish those records on the internet if AmeriCash Advance does not pay us by next Tuesday," it said.

In a statement supplied to Cnet.com, AmeriCash acknowledged that breach and condemned the alleged extortion attempt that followed, which it said it resisted.

On June 12, AmeriCash Advance received a fax, telling us that part of our website had been hacked. The letter went on to demand initial payment of $15,000 from us. We immediately notified the appropriate authorities and promptly took steps to ensure that no other data could be accessed. We will not cave in to blackmail, and are cooperating fully with the authorities to protect our customers and bring these criminals to justice.

AmeriCash added that it was in the process of notifying affected customers, warning them to be vigilant about possible follow-up phishing attacks or other malfeasance.

In response, Rex Mundi said it didn't need to "hack" into AmeriCash Advance's system because they were left wide open for anyone to enter.

AmeriCash Advance is yet to respond to our request for further comment on the breach. ®