Pro-Islamic State hackers hijack US military social media accounts, proclaim 'CyberCaliphate'

The Pentagon is investigating how hackers claiming to be aligned with Islamic State took over US military social media accounts and released more than half a dozen documents - some with the home addresses of retired generals.

In an embarrassing propaganda setback for the United States, a black-and-white banner with the words "CyberCaliphate" and "I love you ISIS" replaced Central Command's usual logo on Twitter and YouTube on Monday before the pages were suspended.

But the US military downplayed the effect of the hacking, saying no sensitive computer networks were penetrated and no state secrets were revealed.

"Our initial assessment is that no classified information was posted and that none of the information posted came from Centcom's server or social media sites," the command said.

The command has notified law enforcement agencies about "the potential release of personally identifiable information and will take appropriate steps to ensure any individuals potentially affected are notified as quickly as possible", it said.

The hacked Twitter feed posted what appeared to be a phone directory of officers that was slightly out of date.

The Pentagon, which devotes a great deal of effort to its social media accounts, said the incident amounted to mere digital "vandalism".