In response to a recent flurry of offensive "spam" postings in several blogs here (mine included!) I offer Clusterbloggers the following advice (below) and please rest assured I'm still working to improve the security settings. This is new software to me and I'm still learning all the bells and whistles. 
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I have attempted to reset the overall blog spam blocking settings to cut off posts like this and this should hopefully have an immediate effect: unfortunately, as any blogger will tell you, having an "open" internet journal where anyone is able to find it, read it and post a message attracts spam and offensive messages as a matter of course. It is the pay-off for being able to share your valuable opinions and information with the world and inviting the world to share back!
These new spam settings may also mean that perfectly inoffensive posts you make that by chance contain some banned word or combination of words may be removed or moderated. Please bear with me as I attempt to get the balance right.
A couple of things you can do with your blog to slow the ability of spammers to post: it attracts extra work for you but is worth it.
- Go into the Settings Menu for your blog, then Advanced Post Settings, then the Override/Globals tab. Choose "All Comments Require Approval" from the dropdown box and save your settings.
- When making a new post, make sure you go into the Advanced Options tab and choose "All Comments Require Approval" from the dropdown before posting.
Both of these options will mean that you will have to login and approve even legitimate posts, but it should also mean that you can delete any spam postings before they are visible on your blog.
You can of course use the above settings modifications to turn off the comments posting function on your blogs entirely, but as Rebecca has said (quite rightly), that defeats the object of blogs as an interactive resource.