Mike is using Terminal on his Mac and he's noticing a strange name at his command prompt. A day later it disappeared. Leo says that the public name of his computer may have been changed. He can learn how at osxdaily.com.
It could have also been a host name that the computer was logged into, and that could indicate malware at work. Leo recommends installing Little Snitch. It will monitor any outbound connections that are occurring and show him which apps are phoning home. That could give him an idea who's messing with his Mac.