FBI warns 'Anonymous' hacked US government sites for year

Hackers linked to Anonymous group secretly accessed US government computers and stolen sensitive information.

The FBI warned that the information was stolen in a campaign that began almost a year ago.

According to the Guardian, the hackers exploited a flaw in Adobe Systems Inc's software to launch a rash of electronic break-ins that began last December, then left 'back doors' to return to many of the machines as recently as last month.

The news comes a day after an Anonymous activist received a 10-year sentence for his role in releasing thousands of emails from the private intelligence firm Stratfor, the report said.

Jeremy Hammond told a Manhattan court he had been directed by an FBI informant to break into the official websites of several governments around the world, the report added.

Accordign to the reprot, the FBI memo about the Adobe Systems attacks described the attacks as "a widespread problem that should be addressed".

It said the breach affected the US army, Department of Energy, Department of Health and Human Services, and many more agencies, the report added.