So did you hear the one about the fangirl who was outed by another fan?

There aren't many rules in fandom.  Cygnet offered up a quick rundown a few weeks ago, but apparently at least one of them is worth a revisit.  From her essay:

7) Don't "out" the fanfic writers.

Fanfic writing is a bit hinky, at best, in mainstream circles. If you have a friend who writes fanfic, please don't tell their coworkers, family, and real life friends how much you love their adult fanfics, at great length, with details. You may think that gushing about the fanfic writer's work is flattering, but to the fanwriter, it can cause moments of acute awkwardness and humiliation.

This is sage advice, young fanthing.  So let me repeat with emphasis: WE DO NOT OUT OTHER FANS.  (I would emphasize this with sparkly text, but the .gif macro doesn't work well on our site.)  Don't do it to n00bs.  Don't do it to BNFs.  Don't do it to your best friend or your fandom enemy.  Don't do it to the pros who are hanging out with us.  (Unless the pro has stated point blank in her user profile "Hi!  RabidFangrrrl is the username of Jane Celebrity aka ME!  Welcome to my blog!"  You're probably okay in that case.)

Real life humiliation is one thing, losing your employment and/or getting sued is quite another.  We inhabit a grey area, and one Google search by a manager can mean the difference between Suzy Fangirl getting a job and being passed over for someone whose personal website is filled with pictures of his cat.  Also consider that occasionally, TPTB get their noses in a sling about the adult-oriented material abounding on the Net, featuring their trademarked characters.  It's much easier for them to go after Suzy Fangirl's real name than some LJer named ILurveNekkidWinchesters.  And if you're the one posting on a message board, blog or wiki that the two are the same, you're the one causing the problem.

A note: it is your responsibility to guard your privacy online.  Always be sensible, use a handle rather than your real name, don't give away personal details online that you wouldn't feel comfortable shouting in a subway, assume that anything you post will be read by people you do not know even if it's locked, and until proven otherwise, do not dismiss the notion that the person you are talking to is a forty-year-old perv (or possibly an FBI agent).  If you're posting smut, consider getting a second handle that can't be too easily linked with your primary username.  This is common sense for operating online.

That said, posting real-life information about someone else without their express permission, be it their real name or home address, can open you up to a world of hurt.  First, it's a violation of the Terms of Service at many journal sites (including Livejournal) and may get you banned, especially if people get screencaps of the incident before the mods delete the entry.  Second, it's a violation of basic fandom etiquette, and it will get you kicked out of usergroups and shunned by fandom as a whole, just like the people who try to get paid for their fanfic.  Third and most importantly, it's a violation of basic human decency.  It puts you on par with the scumbags who scratch telephone numbers on public restroom stalls with "For a good time, call."  My telephone number may be in the phonebook, but if you're giving it out to random strangers and I find out, my fist will be having a very short conversation with your nose.

It's hard.  I understand it's hard.  OMG, you just found out that your favorite fanfic writer ever is also a published author, and you want to share it with everyone.  But unless she told you that and then gave you explicit permission to go tell the world, you need to treat that information the way you would an email from a friend telling you that she's just been diagnosed with ovarian cancer.  Private info.  Small audience.  No announcements, especially not on her Wikipedia page or her favorite message board.  It's just rude.

Fandom is and should be about the shared squee.  It's about the things we love to discuss together and the places we hang out in bunches, and the stories we tell one another, and the games we make up, and sharing the good and the bad and the weird with the friends we never dreamed we could have.  If you go out in search of private information on other fans and make that public, you're going to make things less friendly for everyone.  You're going to send people running and hiding, because their teachers and students and bosses and school-aged children and next-door neighbours might find out about our fun and disapprove enough to make our lives too difficult to come play anymore.  You're going to wind up being the biggest fish in the pond after all, because everyone else is gone.

Think before you post, always, and if someone points out you've posted something that crosses that privacy boundary, take it down, apologize, and try to do better next time.  Don't be a jerk.