The security of some 90,000 e-mail addresses may have been compromised by the computer break-in at consulting firm and defense contractor Booze Allen Hamilton, Stars and Stripes reported.
AntiSec announced Monday it had infiltrated the firm's servers in an online statement.
The group said it was able to run its own application and found "a list of roughly 90,000 military e-mails and password hashes."
In a statement via Twitter, Booz Allen Hamilton declined to offer further details on the incursion.
"As part of Booz Allen security policy, we generally do not comment on specific threats or actions taken against our systems," the post said.
Earlier this year AntiSec claimed responsibility for breaking into the servers of computer security company HBGary Inc. after the company said it would help track down hackers.