ISPs Need To Keep Moving Against Spam

By Larry Seltzer  |  Posted 2005-02-03 Print this article Print

Opinion: ISPs have to do more than just pass traffic on to the Internet or they're going to be sorry. The blacklisting wars are on their way.

Back in June of 2004 I argued that ISPs need to start rate-limiting use of their outbound SMTP servers. I was right, although for reasons that were a little off. But its a good example of a larger point worth making: ISPs need to be diligent in fighting spam, not just inbound but outbound as well. Ive been looking further into AOLs claims of success in fighting spam, and I find Im believing the claims more and more. Ive been asking AOL users I know, and they agree that spam through to their inboxes has gone down dramatically over the last year or so, to 1 or 2 messages a day. How does AOL do it? Every way they can.

Lets go over a bit of history of how spammers have operated. In the beginning, they simply bought blocks of IP addresses and set up servers and spammed from them, operating like everyone else on the Internet. Then anti-spammers got the idea to blacklist the IP addresses of spammers. As imperfect as this method was (it caused much collateral damage), it impeded spammers, as did the ISPs refusals to sell them more accounts. Eventually, the spammers moved on.

The next technique was to search for open proxies on the Internet, generally e-mail servers that are left open to anyone to send mail, and to a lesser extent Perl mail forms on Web pages with no security on them. Eventually the good guys also got good at blocking these and even at blacklisting the remaining open proxies.

Then the era of the zombied machine was born: Generally through infection by Windows e-mail worms, spammers created backdoor programs on users systems so that the computers could be used to send spam. The worms have their own SMTP servers built in partly for the purpose of propagating themselves, but also for sending out spam. Spammers control large networks of these infected systems; its generally agreed that there are zombie networks with tens of thousands of systems in them.

For insights on security coverage around the Web, check out Security Center Editor Larry Seltzers Weblog.

AOL has been aggressive in trying to block mail from these zombie systems. They have implemented and tried persuading other ISPs, especially consumer broadband ISPs like Comcast that have a history of being abused by zombies, to TCP block port 25 (SMTP Mail) on consumer systems other than through their own mail servers. This is not necessarily an easy thing for an ISP to do, but there are a few ways to do it, including at the cable modem in some cases.

Next page: rDNS and other screws to tighten

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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