As your site grows, you may find yourself granting backend permission to more and more people who are helping you with the site. That’s a great way to take on new projects and bring in people who have skills different from your own. However, it also opens up the potential for a security hole.  For starters, it’s important to only give new users permission to access the things they will need in order to do their work. Don’t grant overall admin permission to anyone who doesn’t need such wide-ranging access. Even if you trust the person, play it safe and only give them access to what they absolutely need.  Also, when a person is done working with you on the project, remove their credentials entirely so they can’t log back in later. Again, this is just a precaution, and you should take it even with people you trust. WordPress security is all about plugging as many potential sources of trouble as possible, even if they don’t seem like a major threat.