Stratfor warned of the attack--which exposed online names, home addresses, and credit card information of 4,000 of the firm's clients--on its Facebook page Monday.
Stratfor, which gathers intelligence data to provide analysis for a variety of companies, warned clients that their information may have been compromised and provided information on its Facebook page for how they can report any unauthorized access.
However, it denied that a "private client list" Anonymous posted on its Pastebin site was indeed that. Stratfor said the list was merely clients that have purchased some of the firm's publications and is not an exclusive client list.
[ Success of hacktivist attacks have caused many to wonder: Can Anonymous Cripple Critical U.S. Infrastructure? ]
Government and related entities found on that list include the Department of Defense, including the Army and Air Force; the Departments of Justice, Energy, and Treasury; and defense contractors such as DRS Defense Solutions and Total Defense Logistics.
Anonymous claimed responsibility for the attack on its Pastebin page and also kept a running play-by-play of its activities on its Twitter feed. The group said it planned to use the credit cards to steal money to make a variety of Christmas donations.
Indeed, some of Stratfor's clients said they experienced unauthorized transactions on their credit cards, according to a report in the Wall Street Journal.
Along with related groups like LulzSec and Anti-Sec, Anonymous made headlines this year with a spree of high-profile, politically inspired attacks that targeted government agencies, among others. Government contractors Booz Allen Hamilton and IRC Federal were among those targeted in that spree.
The hacktivist groups appear to be gearing up for another wave of attacks. Anonymous warned that the Stratfor attack would be the first in a Christmastime torrent of attacks it's mounting called "LulzXmas."
To help clients who have been affected by the breach, Stratfor said it has retained an identity theft protection and monitoring service and will email clients with information about the service by Wednesday.
Stratfor's website remained offline Tuesday, as it has been since the attack was discovered.
In this new Tech Center report, we profile five database breaches--and extract the lessons to be learned from each. Plus: A rundown of six technologies to reduce your risk. Download it here (registration required).