This is what happens when you allow non-logged in users to comment on your blog (androidscreenshots.com)

This is my website. I never really got it off the ground as I focused my attention on other projects. But, I never took the site down. Like an abandoned building, it slowly decayed in a somewhat interesting way. The site now shows what happens when you allow anyone to comment for 2 years. You get 17,000+ spammy comments.

In case you were wondering, this is a good reason why you need to mandate login before allowing comments on your website.