function wp_blacklist_check( $author, $email, $url, $comment, $user_ip, $user_agent ) {
	/**
	 * Fires before the comment is tested for blacklisted characters or words.
	 *
	 * @since 1.5.0
	 *
	 * @param string $author     Comment author.
	 * @param string $email      Comment author's email.
	 * @param string $url        Comment author's URL.
	 * @param string $comment    Comment content.
	 * @param string $user_ip    Comment author's IP address.
	 * @param string $user_agent Comment author's browser user agent.
	 */
	do_action( 'wp_blacklist_check', $author, $email, $url, $comment, $user_ip, $user_agent );

	$mod_keys = trim( get_option( 'blacklist_keys' ) );
	if ( '' == $mod_keys ) {
		return false; // If moderation keys are empty
	}

	// Ensure HTML tags are not being used to bypass the blacklist.
	$comment_without_html = wp_strip_all_tags( $comment );

	$words = explode( "\n", $mod_keys );

	foreach ( (array) $words as $word ) {
		$word = trim( $word );

		// Skip empty lines
		if ( empty( $word ) ) {
			continue; }

		// Do some escaping magic so that '#' chars in the
		// spam words don't break things:
		$word = preg_quote( $word, '#' );

		$pattern = "#$word#i";
		if ( preg_match( $pattern, $author )
			|| preg_match( $pattern, $email )
			|| preg_match( $pattern, $url )
			|| preg_match( $pattern, $comment )
			|| preg_match( $pattern, $comment_without_html )
			|| preg_match( $pattern, $user_ip )
			|| preg_match( $pattern, $user_agent )
		) {
			return true;
		}
	}
	return false;
}