The Ministry of Defence's administrative system has been infected with a virus, the MoD said on Friday. After a clean-up operation, some systems are still affected.
The administrative system is used by the army, navy and air force. Navy warships including the Ark Royal were affected, an MoD spokesperson said in a statement.
"We can confirm there is a computer virus affecting a small number of MoD systems; however, there is no impact on operations," the spokesperson said. "Immediate action has already been taken to clean up the infected systems and protect them from re-infection."
While the number of systems infected was limited, the whole MoD email system had been affected by outages, the spokesperson said. Internet access had also been affected. This was due to the MoD turning off parts of the system while they cleaned the infected machines, said the spokesperson.
The MoD was confident the infection was not somebody trying to infiltrate the MoD, said the spokesperson, who added that personal data had not been compromised.
The infection first occurred on 6 January, and meant some MoD staff were without network access. The MoD is investigating whether any payment systems were affected.
Earlier this week the secretary of state for defence admitted that only 27 percent of MoD IT systems fully meet government security guidelines.