Hackers have attacked the computer network of a US military contractor and stolen 90,000 email addresses, the Telegraph reported.
A wing of hacking group Anonymous said it had broken into the systems of Booz Allen Hamilton and then posted the details on the internet.
The daily said the hackers were "apparently only able to get encrypted versions of the email passwords". Around 53,000 of them carried the military ".mil" domain.
The hackers also wiped out four gigabytes of the Booz Allen source code in the attack they called "Military Meltdown Monday".
"We infiltrated a server on their network that basically had no security measures in place," the group said in a statement.
Booz Allen provides technological services including cyber-security consulting to the US military and other government agencies.
A spokesman said its security policy meant "we generally do not comment on specific threats or actions taken against our systems".
The hacking group later responded with the comment: "You have a security policy? We never noticed."
Anonymous has earlier hacked companies like Amazon, Bank of America, Mastercard and Visa.