A hack forced the massive U.S. mortgage lending business Mr. Cooper to shut down its IT infrastructure, including its online payment interface.

Based in Dallas, Texas, Mr. Cooper (formerly Nationstar Mortgage LLC) is a mortgage lending corporation with 4.1 million clients, employing around 9,000 people. With $937 billion in loans under service, the institution has grown to be the biggest servicer in the country.

Clients complained yesterday that they were unable to access Mr. Cooper’s website in order to make loan or mortgage payments. Rather, a message informing them of the company’s technical outage met their arrival.

A note on Mr. Cooper’s website stated, “We are experiencing a system/technical outage, and we hope to resolve this soon.”

“While we strive to resolve this issue, customers attempting to make payments won’t be charged fees or experience any negative effects. We sincerely regret any trouble this may have caused and promise to keep you informed on a frequent basis.”