There are a number of diferent Proxy grading systems, each one has diferent ways to grade whether or not a Proxy is infact Anonymous and how Anonymous it is. A Level 1 Proxy by definitions exhibits absolutely no leekage of variables, and also has the unique property that there is no RDNS records for its IP. This means that if a Proxy is lets say 203.129.16.4 and when you do a dns lookup on it, you will get no hostname. The primary diference between Level 1 and 2 is that Level 2 does indeed have a resolvable hostname. As far as Level 0 goes, I would personally view this as stating the Proxy is not Anonymous and therefore does not indeed have a Level, or atleast that level is undeterminable at the server side level, and instead of the level being defined as '?' it is defined as '0' as the variables do not spill the IP Address. If you check the specification of Proxy Judge 2.35 then you will see that the only levels it will display are "?,1,1?,2,2?,3,3?,4,4?,5,5?". So either the program you are using cannot decide on what Level the Proxy is, or it is its own way of stating the Proxy is not Anonymous. I would suggest a manual check of your results to see exactly how your program in question defines its Levels.