As I said in the help forum, the ban system bans users completely from the forum, so it's possible to ban *everyone and anyone* by accident.
The way you ban a user is by clicking on the user's name in the post, click "administrate user" beside their name, then go to the bottom of the page, there are two parts:
Basic Tools (from the drop down, select BAN by IP)
Delete User (delete all posts)
That's 100 times faster than trying to delete every post individually. But you have to be absolutely sure the user is only a spammer, as it's a point of no return.
The workaround for this was for moderators to pitch the spam posts into the "trash" folder and let the forum auto delete them. This does nothing to ban them though.
I'll give McDuffies access to the ban and delete function and we'll see what happens.