When I clicked on my Ubuntu power (start?) button on the top-right corner, a user account by the name of "J Random User" appeared on the list of users in-between the Guest account and my main account that I'm currently using. I restarted my computer and now the user account has disappeared. Should I be worried that my computer has been compromised by someone/something, or is there a logical explanation for this?
Edit: Just to clarify, I'm currently using Ubuntu 13.10.