> Using various tools you can convert the IP number to a domain name. I use
> whois.arin.net to do my lookups. If you don't have whois software you can
> go to:
>
>   http://www.arin.net/whois/arinwhois.html

ARIN works for the Americas, but you also need www.ripe.net for Europe
and Africa and www.apnic.net for Asia/Pacific.