The options on this blog have now been changed to protect it from "Comment Spam" (not that we get many comments anyway!) Anyone can now post, you will just have to pass the "word verification" option. Any known comment spam will be forwarded to Google for their attention - perhaps they, Bill Gates, Steve Jobs and the whole Linux community can get together and rid the world of spam. Or Not.
What is the word verification option?
The "word verification" option can be found on the Settings | Comments tab for your blog, and it looks like this:
If you choose "yes" for this setting, then people leaving comments on your blog will be required to complete a word verification step, similar to the one presented when you create a blog:
What this does is to prevent automated systems from adding comments to your blog, since it takes a human being to read the word and pass this step. If you've ever received a comment that looked like an advertisement or a random link to an unrelated site, then you've encountered comment spam. A lot of this is done automatically by software which can't pass the word verification, so enabling this option is a good way to prevent many such unwanted comments.
(By the way this is called a CAPTCHA - a cutesy acronym that stands for "Completely Automated Public Turing test to tell Computers and Humans Apart".