Richi'Blog
Stuff 'n' nonsense about email, spam, travel, and life in the UK.

Friday, January 19, 2007

Symantec: Spammers Forge Phony Newsletters, Trying to Fool Filters

It seems that spammers have a new tactic in their war to get their unwanted... uhhh... content through our spam filters: forged newsletters.

What they're doing is sending messages that look like legitimate newsletters. Nasty. Examples seen so far appear to be from well-known brands such as 1-800-Flowers, Kohl, U.S. Airways, and "a fantasy football league" [Statto the spammer?].

There's no suggestion that the spammers have broken into the sending systems used by these brands. They just seem to be cloning legitimate content and modifying it. In the same way that phishers modify a bank's legitimate transactional messages to link to their own site, these spammers are taking copies of legitimate newsletters and tweaking them to include their spamvertisements.

But why go to all that trouble?

The idea is to take advantage of people's abhorrence of false positives. Spam filters will be carefully programmed, trained, or whitelisted to let legitimate newsletters through. If a spammer can make their spam look like one of these newsletters -- especially a widely-read newsletter -- they can get through the filter and in front of the user's eyes.

The spammers only seem to be testing the tactic right now -- it's at a very low level, but the theory is that if they find this is an effective trick, we'll see it a lot more.

I've not seen the test runs in my overflowing spam traps -- credit for discovering the phony newsletters goes to Symantec. I guess it takes a large organization, with 24x7, follow-the-sun labs to really keep on top of new developments in spam tactics. It's the speed of identifying these sort of early indications that separates the men from the boys, as it were.

Update: Symantec sent a picture to illustrate. Wasn't that kind?

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Thursday, January 18, 2007

Port 25 Blocking is NOT a Panacea

Increasing numbers of ISPs block the outbound SMTP port 25, requiring all outbound email to go through the ISP's official MTA, using SMTP authentication. However, ISPs that have implemented port 25 blocking shouldn't rest on their laurels.

The basic problem with port 25 blocking is the ability of botnets to subvert it. Once a PC is compromised, there's nothing to stop the virus from submitting spam to the official ISP MTA, using credentials stolen from the Windows registry or keyboard monitoring.

While port 25 blocking is useful if an ISP's only defense is outbound spam filtering, ISPs should do so much more. For example:

  • Cooperating with reputation services that list IP ranges that have no business sending unauthenticated-direct-to-MX, such as Spamhaus's new PBL
  • Recording the volumes of outbound port 25 traffic -- a sharp increase from the historical trend can indicate infection
  • Monitoring blocked attempts to use port 25 to outside MTAs -- another indication of infection
  • Disrupting botnet command and control messages
  • Moving infected PCs into a "walled garden", which prevents them from sending email, surfing the Web, or using other Internet applications until the problem has been cleaned up

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