\_ They are probably running in stealth mode.  
\_ They do not reply to pings.
\_ 
\_ I would probably recommend to drop all packets coming
\_ from that host.
\_ -> [...]
\_ -> The IP address hasn't changed, ip 146.83.240.200 is telling 
\_ -> you that it can't
\_ -> reach that host.  That is the last system in the route to 
\_ -> get to 200.1.28.20.

Consider also that it may be spoofed, and that perhaps your default
policy should be DENY or REJECT.  :-)

David