We've done everything we can to make people feel secure about using the site. Technically, it's safe — people have to be logged on to the site to see any stories, so submitting a story for critique here does not mean it's "published online".
Your story is accessible by the members of Critique Circle. There are different levels of accessibility, which you pick when you send your story. You can have the story visible to all members, only those who have critiqued, or only those who have critiqued recently.
After the crit week has passed, you can hide your story, so nobody else can see it, or you can delete it from the site.
For those who would like to work in a private critique group where everybody knows each other, there is the option of supporting the CC with a small donation, and receiving premium privileges in return. The Premium privileges include the possibility of creating your own private queue and forum. That way you can be sure that nobody outside your own crit group can see your stories.