New user "test" account just showed up
2017 Retina 5K iMac running High Sierra 10.13.3
I woke my computer from sleep this evening. Normally, waking from sleep presents me with a screen to enter my user password. It normally doesn't give me an option to choose a user account because I'm the only user on my computer.
Tonight, I was presented with two user accounts to choose from: mine and one called "test". I checked with my family, and no one's been on the computer or would have messed with any user account settings.
Is there something in a High Sierra update that would have done this? Has someone hacked into my computer from outside (through my home wifi network) or something? Is there anything in MacOS that would explain this?
I've already deleted the "test" account in Users & Groups and turned off the "Guest" network on our Time Capsule (the one that didn't need a password), but I'm really worried here. Anyone have any ideas how this could have happened -- at least, reasons that would be benign?
iMac with Retina 5K display, macOS High Sierra (10.13.3)