Over the last ten days, a series of massive denial-of-service attacks has been aimed at Spamhaus, a not-for-profit organization that describes its purpose as "track[ing] the Internet's spam operations and sources, to provide dependable realtime anti-spam protection for Internet networks." These attacks have grown so large—up to 300Gb/s—that the volume of traffic is threatening to bring down core Internet infrastructure.

The New York Times reported recently that the attacks came from a Dutch hosting company called CyberBunker (also known as cb3rob), which owns and operates a real military bunker and which has been targeted in the past by Spamhaus. The spokesman who the NYT interviewed, Sven Olaf Kamphuis, has since posted on his Facebook page that CyberBunker is not orchestrating the attacks. Kamphuis also claimed that NYT was plumping for sensationalism over accuracy.

Sven Olaf Kamphuis is, however, affiliated with the newly organized group "STOPhaus." STOPhaus claims that Spamhaus is "an offshore criminal network of tax circumventing self declared internet terrorists pretending to be 'spam' fighters" that is "attempt[ing] to control the internet through underhanded extortion tactics."

STOPhaus claims to have the support of "half the Russian and Chinese Internet industry." It wants nothing less than to put Spamhaus out of action, and it looks like it's not too picky about how that might be accomplished. And if Spamhaus won’t back down, Kamphuis has made clear that even more data can be thrown at the anti-spammers.

Escalation

Hating Spamhaus has a long history.

Spamhaus is a nonprofit organization based in London and Geneva that was started in 1998 as a way of combating the escalating spam problem. The group doesn't block any data itself, but it does operate a number of blacklist services used by others to block data.

The first of these was the Spamhaus Block List (SBL), a database of IP addresses known to be spam originators. E-mail servers can query the SBL for each incoming e-mail to see if the connection is being made from an IP address in the database. If it is, they can reject the connection as being a probable cause of spam.

SBL tended to be filled with machines that were, for one reason or another, operating as open relays. The protocol used for sending e-mail, SMTP (Simple Mail Transfer Protocol) has a feature that nowadays might be considered rather undesirable: in principle, any SMTP server can be used to send e-mail from any sender to any recipient. If the SMTP server isn't responsible for the message box that a mail is being sent to, it should look up the server that is responsible for the message box and forward the message on to that server, a process called "relaying," and servers that operate in this way are “open” relays.

This is great for spammers. They can use a bogus address for the sender and the victim's address for the recipient, then use any open relay to actually send that message. The open relay will then find the real recipient server and forward the message.

This is obviously undesirable, so most SMTP servers these days apply additional rules. For example, ISP-operated mail servers will often operate as relays, but with some restrictions: they'll only allow relaying if the connection is being made from an IP address that belongs to the ISP. Or they will require a username and password to access.

As awareness of the problem of open relays has grown and the number of useful open relays has dropped, spammers have moved to other approaches. Instead of sending mail through a relay, they more commonly send it from machines they control directly to the recipient's mail server.

One way they do this is with compromised PCs organized in botnets. The command and control servers direct the PCs in the botnets to send spam, and so the spam originates from hundreds of thousands or millions of compromised home and office PCs. This is why the destruction of large botnets often results in a drop in the number of spam messages sent.

To counter this kind of thing, some blacklist operators operate blacklists of "client" IP addresses, addresses used by consumer-focused ISPs that, for the most part, shouldn't be directly sending mail at all (instead, they should be routing mail through their ISPs' respective mail relays). Spamhaus operates such a list, separate from the SBL, calling it the Policy Block List. Spamhaus also has a database of compromised machines, the Exploits Block List, that lists hijacked machines running spam-related malware.

Spamhaus has a number of criteria that can result in an IP address being listed in its database. The organization has a number of Spamtrap e-mail addresses; addresses which won't ever receive legitimate mail (because nobody actually uses them). This is the most obvious source of IP addresses, and probably the least controversial—if an IP address sends spam to an inbox, it's fair game to regard that IP address as a spam source.

Spamhaus also blocks "spam operations," which is to say companies it believes make a business of sending spam. It lists these in its Register of Known Spam Operations (ROKSO), and it will pre-emptively blacklist IP addresses used by these groups. (Spamhaus will blacklist "spam support services"—ISPs and other service operators known to be spam friendly, for example by offering Web hosting to spammers, hosting spam servers, or selling spam software.)

The organization's most severe measure is its DROP ("don't route or peer") list. The DROP list is a list of IP address blocks that are controlled by criminals and spammers. Routers can use these to block all traffic from these IP ranges. Rather than using DNS, this list is distributed as a text file, for manual configuration, and using the BGP protocol, for routers to use directly.

In addition to the lists it maintains and the different inclusion criteria, Spamhaus has one particularly important policy: escalation. Repeated infringement—such as an ISP that refuses to terminate the service of spammers on its network—will see Spamhaus move beyond blacklisting individual IP addresses and start blacklisting ranges. If behavior still isn't improved, Spamhaus will block ever-larger ranges.

All of these policies, predictably, have caused conflict.