The US State Department's computers are vulnerable to hackers who could steal or change data or close whole systems down, a congressional report said on Tuesday.

The General Accounting Office investigation, which looked only at unclassified systems, found them "vulnerable to access, change, disclosure, disruption or even denial of service by unauthorised individuals".

The report said the State Department, which oversees US foreign policy, should establish a central unit to control security of the information systems, undertake regular risk assessments and take a number of other steps.

It said the department has a number of unclassified systems which hold personnel, pay and health records as well as diplomatic agreements and communications.