Yup ditto above about the blank record. In a lead record, you should probably look at the original source type: in this case it 'll be Web page visit or salesforce.com
If you look at the original referrer, say if someone clicked on your google adword campaign, this original referrer field might show http://www.google.com or doubleclick.net.
You might also see your marketo landing page as an original referrer.