I would like to know this too. A storm just blew through my area and my power went out. When it came back up, the router lost ALL settings, including password and the security settings. A bunch of strange connections showed up in the advisor. I saw what had happened and created a new encryption ticket... but all those foreign devices are still showing up. I want them purged so if for some reason my security settings ever drop again, I'm going to get alerts for those mac addresses.
I'm really surprised I can't click on any of those items and just pick "remove from network" or better, "block intrusive device" on them.