Can I encrypt data in a way that it can't be copied or edited? - Super User

As an attempt to make this interesting (by completely ignoring it):

It turns out that, by employing quantum mechanics, it's possible to encode data and then later answer the question "has anyone looked at the data yet"?

Let's say you're a secret agent. You get your instructions from shadowy figures in paranoid places. And, being a secret agent, it would obviously be a problem if anyone were to eavesdrop on the instructions sent by your employers. Quantum entanglement allows you to check: has anyone already looked at this message?

Pretty neat!

Why's this on HN? We all know the answer to this.