TrackbackValidator: sneak preview
The idea behind the paper and the plugin is simple: the sites linked to by TrackBack spam never contain a link back to your blog entry, but nearly every legitimate blog entry that pings you does. Therefore, rather than fancy content filter, we can eliminate TrackBack spam by simply fetching the URL in the ping and only accepting it if the page actually contains a link to your site.
This plugin implements that idea. It also includes options to white-list all pings coming from your domain and to allow ping that link to files under your entry (e.g. an uploaded file or the comments page) rather than just the permalink. My spam rates have been way up lately, so I'll be uploading this tonight and we'll see how it goes.
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