forgive me if I get the names wrong, its been a while since I looked lol..
but if you are talking about the one named
www.AvaMods.com, thats a HLTV client..
if you mean the "Playing AvaMods Since 2007" that is nothing to worry about either, thats a client based on the server machine itself and no one is actually playing on it.
..if you mean there is someone else though, let me know the name or steamid and I can try and make some time to look into it