Unfortunately, occasionally SPAM comments are part of online writing.
You have the option to set each Hub such that comments must be approved before they show up.
You can also set them to only allow comments from logged in users.
I suggest setting your Hubs such that you have to approve comments.
http://hubpages.com/my/hubs/comments (see Show Settings)
You can then review the comments periodically and mark those SPAM that are.
The system then uses this information to help identify SPAM comments going forward so you can help other authors and yourself by marking SPAM comments.