Ounce of prevention: Adam Kalsey is in a war against comment spam, and he shares some great ideas here:
“What will probably be the biggest help is the thing that was easiest to do: changing the comment script name.What else would be effective is changing the names of all the form fields. Making them short random strings would make it impossible for a bot to recognize the comment form using only the field names. People would be able to understand the form because of the labels, but bots would have to implement a large amount of fuzzy logic in order to recognize that ‘Name,’ ‘Your Name:,’ and other forms are really the same thing.”
Unwanted Comments: Comment spam is becoming a bigger and bigger problem. Shirley has a good roundup of resources to help you fight it. "Some site owners stave off comment spam by closing off older comments, using blacklists, using filters, just deleting them when they occur, or a combination of these.…