I posted about Trackback Spam previously but it was brought to my attention that I didn’t explain it properly, so I am now going to attempt to rectify that.
If you are using a blogging application, like WordPress, there is a facility called Trackback, whereby, when you are making a post in your blog, and you refer to a post someone else made in their blog, you can add in the trackback uri of their post (normally displayed at the end of their post) to your blogging software, and it will send a notification (called a trackback) to them.
When their blogging software receives this notification (Trackback), it displays the relevant part of the post in the comments section of the site.
Spammers are recently starting to post faked trackbacks directly to people’s blogging software, pretending someone has posted about one of your posts, hoping your blogging software will automatically display their spam on your site (thinking it is a legitimate comment).
The reason they do this is to get links from external sites to their sites, thereby pushing up their all-important Google Page Rank.