Increasing quantities of personal data are recorded and stored on computers: for example, where and when you use your mobile phone or what purchases you make in the supermarket. This poses a potential threat to our privacy. The Data Protection Act forbids the use of this information for a purpose other than that for which it was collected, apart from instances in which serious crime could be prevented or detected. We must not allow this principle to be abandoned because our liberty depends on it. Although at present there is no malign political purpose to which this information is put, we cannot be certain that this will never be the case.