[facebook like box] visitors must login to facebook?

I’m trying this Facebook Like Box plugin‘s widget.
It appears fine on my site’s sidebar.
But all it says is, “login to see this content.”

When I log into facebook then I can see the facebook user logo, the activity stream and the avatars of the facebook user fans.

So do my website’s visitors have to already be logged into facebook to use this widget?

I thought it would make my facebook content visible to all visitors.

??? and help appreciated.