asked Her Majesty's Government:

In respect of (a) the Home Office, (b) the Border and Immigration Service, (c) the Identity and Passport Service, and (d) the Criminal Records Bureau, on how many occasions in the past year malicious programs have compromised departmental 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. [HL2983]

It is not in the public interest or the UK's national security interest 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.