FBI reveals agencies have been under attack since December 2012.
The FBI has warned that members of the Anonymous hacker collective have been hacking computers belonging to US government agencies.
The security service says the hacking began in December 2012, and that Anonymous has since stolen lots of confidential data.
According to a memo from the agency, hackers made use of a defect in Adobe Systems’ software to trigger several electronic robberies, then left ‘back doors’ to enter into multiple computers up until last month.
Describing attacks as "a widespread problem that should be addressed", the memo noted that the breach affected the US Army, the Department of Energy, Department of Health and Human Services, and possibly several more organisations, Reuters reported.
It added that the stolen information included personal information on about 104,000 employees, contractors, family members and others linked with the Department of Energy, together with information related to approximately 2,0000 bank accounts.
Information about the cyber campaign is still being gathered by the investigators, and the FBI believes it is still going on.
The hacking is considered to be linked to the case of a British hacker Lauri Love, who had been arrested over alleged hacking into US government systems by exploiting a flaw in Adobe’s ColdFusion software, which is used to develop websites.