1. Not without specific logging (There's an auditor plugin which does it, or you can increase logging in the admin options and then search your logs for user create)
2. Go into Admin -> Global permissions and look at the "can use Jira" line. All groups there are added to all new user accounts automatically. My general advice here is to have one single group in there that says "these guys are my active users" and use that group for absolutely NOTHING ELSE (unless it really is something you want global, like bulk edit, user lookup or access to the "support this jira" project)
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.