The email addresses of around 19,000 US military personnel and over 200 UK defense officials were among the data stolen from US military analysis firm StratFor by hacktivist group Anonymous and leaked online, according to the Guardian.

Anonymous leaked the data just after Christmas, after claiming that it has successfully hacked StratFor.

A statement on the company’s website says "we are currently investigating this unfortunate event and are working diligently to prevent it from ever happening again. As a result, we have delayed restoring our website until we can perform a thorough security review."

"As a result, we have provided paid subscribers with identity protection coverage from CSID, a leading provider of global identity protection, at our expense for 12 months," it says.

According to data loss prevention specialist Identity Finder, the data contained 50,000 credit card numbers from StratFor customers (most of which had expired), nearly 50,000 email addresses, 30,000 phone numbers and 45,000 passwords for the StratFor site.

The Guardian newspaper commissioned independent research firm the US Cyber Consequences Unit to analyse the data, revealing the extent to which military personnel were exposed in the attack.

On Friday, StratFor revealed on its Facebook page that some customers had received emails falsely claiming to be from the company. "This email, and all similar ones, are false and attempt to prey on the privacy concerns of customers and friends. We strongly discourage you from opening … attachments," it said. "We deeply regret the inconvenience this latest development has created."