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The Measured Effectiveness of Blocking Asian Spam
fadden writes: "I recently started blocking IP addresses in China and Korea that were sending me spam. Instead of a blanket ban, I only blocked the subnets from which spam was being sent. After my first week of scanning and banning, I wrote up
a report on the effectiveness of the blocks." In related news, SSKennel adds that: "The U.S. Federal Trade Commission has discovered (prepare to be amazed!) that revealing your email address in chat rooms can get you spammed. It claims to have taken action against spammers who harvest email addresses and use them to send fraudulent spam." Shocker!
Subject says it all. I block so much spam by using spews.
On the other hand, 15 or so spams a day (in a language I don't even understand) every day is a major waste of bandwidth, and as irritating as hell.
What can we do about this nusiance?
-- And when Justice is gone, there is always... Force. --Laurie Anderson, "Oh Superman"
I started blocking off all Asian Pacific networks about 6 months ago. I wrote a quick Sendmail tutorial about it right here.
How well does this work? Extremely well. I've gone from receiving 20 pieces of SPAM a day to only 1 or 2 (which Spamassassin typically catches. I realize that this method won't work for everyone, but it has worked out quite well for me.
--It's Pimptastic!--
If you're running Outlook 2000 or XP - Cloudmark is a nearly PERFECT solution to Spam - and IT'S FREE (for now, at least).
Yes, there is a difference between regular spam and the fraudulent variety. Normal spam is sent by well known "bulk mailers" (as they call themselves, in a pitiful attempt to legitimize their business) on a contract-for-hire basis.
They send email directly from their own systems to your mailbox. They do not fake their headers, use open relays, hijacked proxies or root'ed boxes of other people to send out their messages. They generally have contracts with their ISPs to not cancel their connectivity as long as they have some type of proof, no matter how vague, that the mail *might* be considered opt-in (and as long as the complaints aren't too frequent. These people do listwash their own lists, if only to stop spamming people who actually complain about it, and also to show to their ISPs that they have an effective opt-out system. Their spam is annoying, but currently legal.
Fraudulent spam, on the other hand, is completely different. These are the people that hijack other people's machines to do the dirty work, rape open relays and consume all of their bandwidth during spam runs, actively probe for open relays and proxies, forge everything they can in the headers, study SpamAssassin and other filters in an attempt to craft messages that don't "look" like spam. These are the people that use their opt-out lists as a source of revenue (by selling the names to other spammers), and will frequently joe-job spam activists and others who complain too loudly and to the wrong people...
The first type of spammer sends out insurance offers, cell phones ads, inkjet ads and such. The second type sends out virus/trojan laden messages, porno by the bucketload, ads for illegal drugs, etc.
Both types of spam are annoying, but the "fraudulent" type is much more so because of its immoral content (and anyone who thinks that sending pornographic images to children isn't immoral should quietly remove themselves from the gene pool) and also because of the theft of services (bandwidth, hard drive space, etc.) from the relays and proxies that they abuse.
I believe they also have a POP3 proxy and an SMTP proxy is on its way. The automation for these is not quite so refined, however.
I hate spews. spews is everything that is wrong with anti-spam work.
There is no way to get off of the SPEWS blacklist, and if they black your entire NSP for one of the NSP's customers... tough luck for you. You can post to a usenet group and beg, and they wont do anything other than tell you to break your legal contract and go elsewhere. 20 people will harass you, and you can't even know which one to listen to.
SPEWS can rot in hell. A properly configured SpamAssassin will block 98% of spam and have 0.01% false positives (I haven't gotten one false positive in a year, but I will someday).
SPEWS is NOT how one prevents spam. SPEWS is how one pisses off the people trying to mail them.
I can't stress enough how much I hate SPEWS and how much it should die.
Please, please don't support SPEWS. I beg you.
A lof of spammers *do* use these HTML mail tricks. However, a lot of plain users send HTML mail, often without knowing it, because Microsoft mail programs send HTML by default. So if you want to read HTML mail safely, do this: block your network connection while opening it. You can unplug the cable, take the mail program "offline", hit the "stop" button on ZoneAlarm, whatever. This won't cause problems with legit HTML mail, because the HTML is usually just for fonts and stuff. But it keeps the spam messages from "phoning home" successfully to get their graphics.
A few months ago my spam level reached the point that made me do something about it. After looking carefully at all the headers, I concluded that about 80% of the junk (mostly from Asia) came from IP addresses with no reverse DNS database entry. (The IP did not resolve back into a hostname.) Just about all reputable mail exchangers have a reverse DNS entry. (The ones who don't are run by the clueless.)
/etc/hosts.deny /etc/hosts.allow file with "sendmail: KNOWN". (Make sure "sendmail" equates to 25 in your /etc/services file.)
/etc/hosts.allow file. (e.g. "sendmail:66.187.232." will allow mail from RedHat.)
I decided to use this to my advantage. You can too.
If your sendmail daemon uses the tcpwrappers library, you can create a
file with "sendmail: ALL" and a
Doing the above will cause your mail exchanger to refuse incoming mail connections from any host with an unresolvable IP address. It will cut up to 80% of your spam.
For the clueless ISPs, you can add exceptions to your
I wish more people would do this.
If you run SpamAssassin after the MTA, sure, the cows are out. Better to run SpamAssassin integrated with your MTA if possible, which can be done with Exim, Sendmail, and possibly others. Doing spam checks at the MTA level also lets you look at the mail envelope data and similar that SA cannot check on.
Granted, you tend to have to run your own mail server to do this, but hey...