These do get shared, but usually in meme form where you turn your birthday into your "Werewolf name" and are encouraged to share in the comments. Because you're sharing in an altered, amusing form, you don't stop to consider someone can reverse your birthday from it.

My birthday is literally already on my Facebook "about" page though, and shown to all my friends whenever it comes around, so they can post on my timeline.

But that doesn't automatically make it available to 3rd parties that have no connection to you.

"Being an American is a privilege few have. Let's share our American issued social security numbers!" <Over photo of a bald eagle>

My understanding is that a portion of the SSN is based on the ZIP of your birthplace. I'm sure some clever person could come up with a way to use birth location + a checksum that would reveal an SSN without actually typing it out.

I'm thinking something like, "Add up all the individual numbers of your SSN and figure out what Founding Father you are!" Use some statistics to ensure that lots of people get good ones.

Used too, But anyone under the age of 20 will have a random SSN [1]

1: https://www.ssa.gov/kc/SSAFactSheet--IssuingSSNs.pdf

The first 5 digits are directly correlated to DOB and birthplace, the last 4 are mostly random. https://www.pnas.org/content/106/27/10975 There's a pretty interesting study done on this.

I presume there are a lot of non-Americans with SSNs: I have one from working in the US on a working visa.

Oh, I've absolutely seen these come up.

"Tag your mother if you love her", "tag your childhood best friend", etc.

- Your teacher in 1st grade (seriously, if anyone knows, please tell!) - Favorite fictional character - First pet

First pet name, born city, childhood nickname are the first 3 questions of Windows 10 local user installation.