Unfortunately spam is everywhere! And what makes matters worse is that when one solution is found, the "spammers" figure another way!
If you have enabled "comments on your blog with the moderation option then you may be quite familiar with the problem. Someone will leave a comment on your blog but also put a link to their "spam" related site! In the worst case scenario their comments aren't even related to your blog post but are just spam altogether!
Unfortunately and as far as I know, you can't just block one person from commenting on your blog - you have to enable the "moderation option so that you can moderate the comments - even if it is only for that one person!
Fortunately I happened upon a solution when I get a spam comment on one of my blogs. It does require a little extra work but it is a good example of turning lemons into lemonade! Actually I like when I get these so-called spam comments because my solution for dealing with them improves my computer skills and also helps with increasing my Adsense numbers too!