Facebook has three types of groups that users can create or join: Public, Closed, and Secret.
Secret Facebook groups are extremely popular, and can be composed of only a few members, or several thousand. The groups cannot be found via a search, and no one outside of the group can see posts, a list of members, or otherwise know that the group even exist.
For these reasons, many members of secret groups post comments and photos that they would normally abstain from. What they fail to realize, however, is that anyone in their group can easily reveal what is being posted. All a group member has to do is screenshot a post or comment, or take a photo of the posts onscreen with a camera. Therefore, the group, and its posts or comments, are only as secret as its members permit it to be.
There are hundreds of stories circulating of employees losing their jobs, marriages broken, and lives disrupted by posts which Facebook users mistakenly thought would not be seen by anyone outside of their select secret group.
All it takes is one disgruntled or offended user in the group, and your secrets are out. Remember that almost anything posted online, even in the most secure environment or program, can be leaked, without any special tools or advanced technology.
Discretion is always advised when posting online…
Here is a simple printout from Facebook that explains the differences in groups.