A unknowen user has poped into my system. I have file shareing enabled for my network and this user has somehow added themself to certian folder shares with full permissions. It is a numeric username and apears it might have been machine generated but I am unsure. Each time this user apeard in my shares I deleted without thinking to take a screenshot. However the user can still be seen in my registry as attached. My administrative tools, computer management does not list this user. And this is what I don't understand.

Can someone help me out, might I have become comprimized, or perhaps a machine generated user for shareing purposes.

Should I be woryed?