There's a very big German webside where you can discuss practically everything, upload art, storys and so on. I registered there years ago and of course said that my gender was female because I had never thought about that in those days.
As I finally realized my transsexuality, I thought nothing would be more easy than to pass on the internet. I didn't thought there would be a problem with that page since they don't state your gender beside your avatar or even on your profile, but lately I found more and more little hints like "Link to her storys" or something like that.
It gets even more complicated since I joined a nice little forum (as male) where everybody knowns each other, and a lot of those people are on the other internet page as well and could stumble across this gender inconsistency.
And you can not change the gender or name (I mean your real name, not username) you registered with. I know I shouldn't be nervous about writing a letter to some help desk, but the people at the help desk are just users like everybody else--it's like telling your teacher and you don't know what he might think about it or whom he might tell...
Besides, it would be the very first time I outed myself as transsexual...