The security panel in Settings allows you to check posted comments for certain values, and act accordingly if a match is found.
Values are matched against every attribute that the Comment provides. This means that values can be words used in the comment, an email address, a URL, User Agent, or IP Address. Matching is case-insensitive.
Comment Moderation
If a match is found, the comment will be marked as pending.
Comment Spamlist
If a match is found, the comment will be marked as spam.
Comment Banned
If a match is found, the comment will be blocked all-together, and not submitted.