The web site of U.S. security think tank Strategic Forecasting Inc (Stratfor) has been hacked and some of the names of its corporate subscribers made public.
Stratfor said the breach came from an unauthorised party. Activist hacker group Anonymous claimed responsibility, but other online identities claiming to be linked with the group claim otherwise.
Stratfor, which describes itself as a provider of strategic intelligence for business, economic, security and geopolitical affairs, said it was "working closely with law enforcement in their investigation and will assist them with the identification of the individual(s) who are responsible.
"As a result of this incident the operation of Stratfor's servers and email have been suspended," the Austin-based company said in an email to customers on Sunday.
Hackers claiming to be the group Anonymous said they had obtained around 4,000 credit card details, passwords and home addresses on Stratfor's private client list, which was posted on information-sharing website Pastebin.
The Pastebin entry lists the names (but not the credit card details) of 4000 organisations, including Australian organisations such as Alcoa, ANZ Bank, BHP Billiton, Griffith University, HSBC Australia, Westpac and Woodside Energy; and IT companies including Alcatel-Lucent, Apple, Cisco Systems, Dell, easyDNS, HP, IBM, Intel, Lexmark, Microsoft, Motorola, Oracle and Unisys.
Stratfor chief executive George Friedman wrote on the company's Facebook page that this was not the company's current client list but "merely a list of some of the members that have purchased our publications."
Friedman recommended all Stratfor clients inform their financial institutions, check their credit reports and lodge an ID theft incident report with the U.S. Federal Trade Commission.
Anonymous, reported to be a loose-knit group of hackers, became famous for attacking the companies and institutions that oppose WikiLeaks and its founder Julian Assange.
Anonymous has also been linked to attacks on the websites of the PlayStation store, the Church of Scientology and governments around the globe that it considered oppressive.
(Reporting By Jerry Norton, Jim Finkle and Nicola Leske; Editing by Dale Hudson).