The information exposed in the breach includes Social Security numbers, bank account data and detailed medical histories, according to Jody Baxmeyer, vice president of marketing at North Regent Rx, the company that has been receiving the faxes.

Baxmeyer said the situation stems from the fact that North Regent's toll-free fax number is nearly identical to one used by Prudential to collect information related to medical claims from doctors across the U.S. The two numbers differ by only one digit, he noted.

As a result, Baxmeyer said, thousands of documents involving more than 1,000 claims have been misdirected to North Regent's office in Lockport, Manitoba, despite attempts by the company to stop the flow of faxes.

North Regent contacted Prudential about the problem in October 2004 -- when the distributor first began operations -- and then followed up last April after it didn't get an initial response from the insurer, Baxmeyer said.

"Prudential's point of view was that 'we are not the ones faxing the information,' which is ridiculous," he said. "They're the ones that solicited the business from doctors and clinics, and they're the ones setting up the protocols for receiving the information."