I can't believe it, but a spam bot was able to modify the very text of the post itself and enter a spam link!
To make it clear, this is not the classic spam in a comment, but this is editing the text of my POST to link to some spammy Ucranian (.ua) site.
Any info and tips to prevent this are very welcome.
PS: I am running WordPress 2.13 and have renamed the comments file to prevent spam (prevents 100% of the spam without the enormous burden on server resources that Akismet imposes), but now the spam bots moved to the very post.