“It’s not as though someone is listening to your phone calls,” says Cluley about the information cell phone companies glean from their customers. “But what they do collect is information about who you rang, how long you spoke to them, and where you were when you did it.”

So even though the conversation is hidden, people can still fill in the gaps, and this can have serious implications. “If you rang a phone sex service at two o’clock in the morning and spoke for 18 minutes, no one knows what was spoken about,” says Cluley. “But I think people can put two and two together.”

But I didn’t sign up for this, is this legal?

Actually, you did, and it is. Each time you log on to a social networking site or use a free online service like Facebook, you’re opting in to having your every move documented just by using the service.

Unfortunately, having access to these conveniences can leave a very detailed data trail behind you, which can easily be pieced together to form a narrative about you and your identity. Just as mobile phone companies have the right to record the metadata of your calls, so do social media companies when you choose to use their services to communicate with friends or followers. Instagram’s privacy policy illustrates what they do with user data by stating under the subheading How We Use Your Information, “….to provide, improve, test, and monitor the effectiveness of our service.”

Not all of these documents are as short, sweet, and to the point, meaning that most people are unlikely to read them. According to the consumer group Which?, Paypal’s total word count for its terms and conditions document is 36,275 words, which is longer than Shakespeare’s Hamlet. Last year, the UK’s House of Commons Science and Technology Committee criticised social media firms like Facebook and LinkedIn for their obscurity and length – the head of the committee describing some of the worst offenders as being "meaningless drivel to anyone except an American trained lawyer”.