HMS Ark Royal has been affected by the virus
A computer virus is continuing to affect the Ministry of Defence's systems but it insists no classified or personal data is under threat.
Up to 70 sites, including several Royal Navy ships and RAF bases, have been affected by the bug, which has shut down computers and knocked out e-mails.
The virus first hit systems a fortnight ago but the MoD says operations have not been affected.
It is still trying to discover how the virus breached its security software.
BBC defence correspondent Caroline Wyatt said one RAF source had said personnel were struggling to communicate with other MoD sites by e-mail, with some having to use pen and paper or telephone instead.
It is not clear where the virus came from, although computer experts said it might have originated in the former Eastern bloc.
Conservative MP Mark Pritchard said he had been told by one defence official that e-mail traffic from some RAF stations had been re-directed to a Russian internet server as a result of the virus.
The MP for The Wrekin, in Shropshire, who is also the secretary of the Conservative defence committee, is calling for a written parliamentary statement on what he called a serious breach of national security.
However, the MoD says it has no evidence the virus came from Russia.
A spokeswoman said it had not been specifically targeted and immediate action had been taken to clean the infected systems and protect them from re-infection.