Wifi security question...

I have a Mac Mini with OS 10.7.4
I get my wifi signal from my Dlink unit downstairs. I added a security code

so I am password protected.. Yet when I go to the "go" heading, go to downloads I see right above "devices" a name quiscuter connected as a guest. How can that be?
Thanks, Rick
--
http://www.photographybyrichardmsmith.com/