Earlier I've studied Chinese domain name scams (part 1 and part 2).
A while ago I read about a study made by Mr. Giovane César Moreira Moura. Actually, the study is his PhD thesis and it is available from his page at University of Twente, Netherlands. Anyway, he claims that roughly 50% of the crap in the Internet is originating from 20 rogue networks. He researched 42.000+ ISPs and found out that e-mail spam, scam attempts, etc. are originated pretty much from the same places. He does not do much finger-pointing, but provides the idea how to produce the results.
His study inspired me to investigate the origin networks of all the crap my honey pot was receiving and do some finger-pointing (I don't have any restrictions about that ). My "honey pot" is a 20+ year old e-mail address. It is in every imaginable spammer/scammer/crap magnet -list. My results are badly skewed: when it receives junk, I'll manually tag it and report it to SpamCop (a spam-protecting service owned by Cisco Systems, Inc.), and eventually blocking the IP-address as a spammer. Since the mail server uses SpamCop blocking-list I won't receive any more junk from the IP, which for studying spammers is not good.
There is lot of evidence that most crap originates from hijacked computers, but not all. Some of spam arriving to me originates from VPS-boxes. I dunno if they are rented with real or stolen credit cards. Anyway, most spam I receive have some sort of forging attempt in the mail headers. So I'm utilizing tracing of non-forged e-mail origin with SpamCop's reporting tool. In his thesis Mr. Moura writes that the ultimate origin is almost always not discoverable. Hiding one's real location is way too easy in the Internet. Closing the sending IP typically helps, but leaves the criminal unidentified.
Anyway, here's my list:
30, IRINN-BROADCAST-ADDRESSES, India
9, GOOGLE, USA
8, PAET-FSS-IMPLI-1, USA
5, FR-OVH, France
3, 66-132-128-0-NET, USA
3, EGIHOSTING-4, USA
2, 1AN1-NETWORK, USA
2, DROPBOX, USA
2, NLYR-ARIN-BLK5, USA
The number is number of e-mails originating from that network followed by the network name. The list was gathered during 90 day period. In the list there were additional 80 networks with only single e-mail originating from them.
Most of the crap I receive originates from India. 2nd biggest seems to be Google. Also a huge virtual server renting company OVH-net is in the 4th place. Others I cannot explain. Another conclusion I can draw from these is that the 20 worst networks are not the ones bothering me.