The details emerged via a tender document published on a government website, seemingly by accident.
The document stated that cyber-security firm BAE Systems Applied Intelligence was called on for “urgent support”.
It is thought that anonymous hackers made their way inside the FCDO systems but were detected.
It is believed that no sensitive or highly classified data was breached.
It is unclear when the incident took place but the contract finished on 12 of January this year and was valued at £467,325.
The tender details were first reported by the publication The Stack. It says that BAE Systems was “the Authority’s long-term service management integrator”.
“Due to the urgency and criticality of the work, the Authority was unable to comply with the time limits for the open or restricted procedures or competitive procedures with negotiation.”