How did you come to "just notice it" ? Did it just appeared at the welcome screen, or have you noticed it elsewhere ? What type of other accounts do you have ?
Compare the accounts shown at the welcome screen with those shown at safe mode. What differences are there, if any ? Do you have family members who could have set it up ?
I've just noticed that I have a user account named ASP.NET which is password protected. Anyone know what this account is. I didn't set it up myself.