zlacker

But the problem is, it IS easy. Even anonymized at assets are de-anonymized trivially,using secondary datasets. You can uniquely identify more than 87% of the US population with gender, birthday, and zip code. For more than 50%, you can use the municipality name instead of zip.

If your friend uses a separate, privately maintained email address for everyone and every service, that will help a lot. Then we only know his identity because email is sent in the clear, even between his own server and home computer. Of course, everyone uses separate email addresses for everyone, right?