Did T-Mobile sell my data?

One of the biggest news of the day has been the illegal sale of personal information by T-Mobile staff to rival mobile companies, so they can 'cold call' T-Mobile customers whose contracts were coming to end. I'm a T-Mobile customer, and for that reason I naturally have an interest in this piece of news. I have had one or two cold callers, but usually I ask them, quite curtly, to remove me from their list of numbers. They don't call back.

It is unclear how much of how many people's data have been sold. So many private companies from supermarkets to online companies and public bodies hold lots of information on us, which in many cases we freely gave, and this makes our lives more convenient but also represents a problem. In each organization, there must be a number of people with access to data, and because such data are valuable and sellable, there will be a temptation to steal, leak and make money.

The choice for us the consumers, unfortunately, seems either accepting this risk of personal data leaking without our consent, or to live on cash only, go off-line, and fill no forms whatsoever. It is not the secret police we need to fear, but the supermarkets who seem to know more about us than we do ourselves.