Apologies to everyone, I meant to blog this when I changed the system.
From last Monday, all comments will now be held for moderation before appearing on the blog. In addition, any comment which does not come with a valid email address will not be approved (unless I know of a reason beforehand).
Passwords for protected posts are only given to people that I know personally, and are offered out to people from time to time. They are never given out to people that email and request them.