Some of you will have heard of link spam - but are unsure of what it is. Well ... I have an example on this very blog. As you will see, anyone can add a comment - but I have the setting so that all comments are emailed to me for 'vetting' so that I can reject unsuitable comments and release suitable ones onto the blog.
Below is one comment I received for moderation.
As you can see if you take a quick look at the blog entry on which the comment is added - the comment has nothing to do with the original entry from me. You will note also that that the 'comment' is full of links to a variety of services offered by this company. This is link spam. It hasn't worked on this occasion because I have not published it [and have marked it as spam] - however, many blogs are not moderated, and so 'comments' like this go live on a multitude of blogs, each with a link to the link-spamming organization's website.