http://red.ngntfwmwovvku6eqi7dzzgzv2wzlvq2cqtqha7ccgzub2xnivsuxnuyd.onion/r/opsec/comments/1mo5szt/isnt_the_first_and_biggest_opsec_disaster_one_can
For example they can find out that you were born and where, perhaps all the info about your parents. However does that link to your current address and other information, does that link directly to your internet accounts? It's just a part of reality, having friends is a security risk as people have information on you, leaving your home is a security risk as you can be spotted and recorded, using the internet is a security risk as it is monitored.