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The Net Takeaway: Referrer Karma


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Referrer Karma · 02/10/2006 02:07 PM, MetaBlog

I’m trying a new referrer blocker that’s popular in the Wordpress world called Referrer Karma.

It looks like it should work cleanly, but if you are having strange experiences when you get here, please let me know at wexler at yahoo dot com.

Dr. Dave has all the details, but basically, the tool uses Curl to pull out the referring link from the header, and if that referring link doesn’t truly have a link to this site, it returns a 403 and blacklists the IP. I can clear the lists or whatnot, but in my tests, it appears to work fine for legitimate linkers.

I am not using Wordpress for this blog, so there may be some bumps but my address is in the sidebar of every page, so just ping me if you have problems.

Update: Dr. Dave now hates Wordpress, so he’s abandoned this little gem. His page is still up, but the file is no longer available from him. It can be found at:*/

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  1. Exactly why is referer spam bad? It clutters the web logs a bit, but it’s pretty obvious (mostly) what’s spam and what’s not in your referer logs.

    Of course, if you publish a realtime referer module on your blog, then I can see why someone would want to referer spam you. However, this plugin can /easily/ be used to perform a DoS attack on a site with very little bandwidth required on the attacker’s side.
    Dossy Shiobara    Feb 11, 07:11 PM    #

  2. Why bad? Pretty obvious?

    a) Referrer spam takes up my bandwidth; about 65% at this point on a monthly basis. I would say that's a problem. Many others agree.

    b) The stuff I get is not pretty obvious what is referrer spam and what isn't. "Pretty obvious" can be tackled with a regex. But these guys are using hacked message boards to post their crap. To me, it looks like a link from a message forum, like so many of my referrers. But when I go to see it, it turns out to be garbage.

    Now, I don't want to block every message board, so what's left? IP blocking in this world of zombies is also impossible.

    Yes, a poorly designed plugin could, conceivably, be used as a DOS, though I know of none which have been. But that problem is easily eliminated by limiting the Curl pulls of a domain to once per time period, say once per hour or nor more than 4 per 15 minutes or whatever. RK has a limiter built in, afaik.

    Take a look at or for more info, or look at the code itself, Referrer Karma is really only 1 main php file. Thanks for posting!
    Michael Wexler    Feb 11, 08:06 PM    #

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