The issue comes from the U.S. military's ".MIL" domain name used for emails, which is commonly mistyped as ".ML," the domain for Mali. The leak has resulted in the exposure of unclassified but sensitive information, such as diplomatic documents, tax returns, passwords and the travel details of top officers, according to an initial report from the Financial Times.
The Pentagon acknowledged the issue in a statement to Fox News on Monday, saying emails sent outside the ".MIL" domain are typically blocked.
"The Department of Defense is aware of this issue and takes all unauthorized disclosures of Controlled National Security Information or Controlled Unclassified Information seriously. DoD has implemented policy, training, and technical controls to ensure that emails from the ".mil" domain are not delivered to incorrect domains. Such emails are blocked before they leave the .mil domain and the sender is notified that they must validate the email addresses of the intended recipients," the Pentagon said.