A group of hackers calling itself Rex Mundi will release client data stolen this week from the Banque Cantonale de Geneve unless they get 10,000 euros ($12,000), a ransom the bank said it won’t pay.

Rex Mundi will publish more than 30,000 e-mails and client records by 6:00 p.m. today if the ransom isn’t paid, the group said in a statement linked from its Twitter Inc. account. Phone numbers, e-mail addresses and e-mails for two individuals were included in the statement as a demonstration.

“If we do not get paid in the meantime, we will post the Banque Cantonale de Geneve #leak tonight on our website,” Rex Mundi said on Twitter today. “We would like to wish a merry tax audit to all the non-Swiss account holders listed in the BCGE files.”

The bank, which is partly owned by the canton of Geneva, said in statements on its website that “little usable information” was stolen, not relating to clients’ financial information. All affected clients are being contacted by their advisers.

Banque Cantonale de Geneve “stands with its decision” to refuse the ransom demand, Helene De Vos Vuadens, a spokeswoman for the bank. “We do not want to give in to the blackmail.”

--With assistance from Thomas Mulier in Geneva.

To contact the reporter on this story: Jeffrey Vögeli in Zurich at jvogeli@bloomberg.net To contact the editors responsible for this story: Elisa Martinuzzi at emartinuzzi@bloomberg.net Heather Smith, Jon Menon