asked Her Majesty's Government:
In respect of (a) Her Majesty's Treasury and (b) Her Majesty's Revenue and Customs, on how many occasions in the past year malicious programs have compromised their computer systems; for each occasion, how many machines were affected; how long it took to remove the programs from the system; and what the impact was on the department's activities.
It is not in the interests of the UK's national security for departments to confirm whether they hold information about attacks against their IT systems. This would enable individuals to deduce how successful the UK is in detecting these attacks and so assist such persons in testing the effectiveness of the UK's IT defences. This is not in the public interest.