Facebook Secret Groups

[jetlagjen]

I am a member of a "secret" group on Facebook. In the past few hours six people were added, but not by anybody in the group. one of the added people was kind enough to mention it and says she didn't know anything about being added, she just started getting notifications about posts there. The new people have since been removed, and in doing so we noticed that most members say "added by..." but these ones didn't.

1) Does anybody know what happened?

2) If you're in any secret groups you may want to check your membership lists!