Security: 22 "anonymous" users registered

I’m in the process of building a new WP site (3.8.1, always latest) with a purchased commercial theme. The site is live on a server, but in a buried location, so technically publicly available, but no one should find it.

I just discovered in the Users tab, there are 22 anonymous users in there, all with usernames like _1Ef3487r and _2DL46fFK. None have e-mail addresses. All are user type: “anonymous” (not admins).

I’m wondering if this is a potential security hole or not.

I am running Jetpack (latest). I haven’t activated JetPack comments, or Akismet, or any other spam catchers yet. There are no comments in the Comments area. I don’t see any comments on the site (although I could be wrong, because there are a lot of pages).

Should I be concerned or are these harmless little things?