Right now the comment settings on this blog are quite straightforward: anyone with a Google account may leave one. This can easily be exploited by spambots and their shady masters- they just have to make a Google account for the purpose. This is what just happened here.
Since the time all my accounts (except, fortunately, my Google account) were broken into and abused, I am extremely cautious about this stuff (and many people should be, and they are not). The spambot came, left a bunch of comments on various old and new posts, then left. I deleted all the comments, end of the story.
On the other hand, I believe I should respect my visitors' right to express their opinion, so no harder measure will be taken (no captcha or moderation will be applied, as I find both inadequate and bothersome). Although the blog generates a lot of "ghost traffic", there is no other trouble present.