Here's a quick and easy method that has pretty much gotten rid of all my spam comments. It stops comments with embedded links from being posted by anonymous users.

// hook comment creation
function wcic_form_comment_form_alter(&$form, &$form_state, $form_id) {
  $form['#validate'][] = 'wcic_comment_exclude_spam_with_link';
}

// function to weed out spam comments with links submitted by anonymous users
function wcic_comment_exclude_spam_with_link($form, &$form_state) {
  $comment_body = $form_state['values']['comment_body'][LANGUAGE_NONE][0];
  if (isset($comment_body['format'])) {
    $comment_text = check_markup($comment_body['value'],$comment_body['format']);
  }
  else {
    $comment_text = check_plain($comment_body['value']);
  }
  if(preg_match("/href=/i",$comment_text)) {
    if(isset($_SERVER['REMOTE_ADDR'])) {
      $user_ip = $_SERVER['REMOTE_ADDR'];
      if(!user_is_logged_in()) {
        $watchdog_message = "Attempted anonymous link, IP: " . $user_ip;
        watchdog("content",$watchdog_message,NULL,WATCHDOG_ERROR);
        form_set_error('comment_body', t('Embedded links are not allowed for anonymous users'));
      }
    }
  }
}

There is a watchdog message that you can use to ban the IP address if you wish. This code goes in your template.php file for your theme. My theme is wcic. You will want to replace wcic with your own theme name.

Here's a quick and easy method that has pretty much gotten rid of all my spam comments. It stops comments with embedded links from being posted by anonymous users.

// hook comment creation
function THEME_OR_MODULE_NAME_form_comment_form_alter(&$form, &$form_state, $form_id) {
  $form['#validate'][] = 'THEME_OR_MODULE_NAME_comment_exclude_spam_with_link';
}

// function to weed out spam comments with links submitted by anonymous users
function THEME_OR_MODULE_NAME_comment_exclude_spam_with_link($form, &$form_state) {
  $comment_body = $form_state['values']['comment_body'][LANGUAGE_NONE][0];
  if (isset($comment_body['format'])) {
    $comment_text = check_markup($comment_body['value'],$comment_body['format']);
  }
  else {
    $comment_text = check_plain($comment_body['value']);
  }
  if(preg_match("/href=/i",$comment_text)) {
    if(isset($_SERVER['REMOTE_ADDR'])) {
      $user_ip = $_SERVER['REMOTE_ADDR'];
      if(!user_is_logged_in()) {
        $watchdog_message = "Attempted anonymous link, IP: " . $user_ip;
        watchdog("content",$watchdog_message,NULL,WATCHDOG_ERROR);
        form_set_error('comment_body', t('Embedded links are not allowed for anonymous users'));
      }
    }
  }
}

There is a watchdog message that you can use to ban the IP address if you wish. This code goes in a custom module or the template.php file for your theme. I'm using a module as this is functionality only. Replace THEME_OR_MODULE_NAME with the name of your theme or module.