Block Spam Comments with Simple PHP Logic

				
					/**
 * Simple Anti-Spam Logic for WordPress Comments
 */
function rcwebkit_block_spam_comments( $commentdata ) {
    // 1. Block comments with more than 2 links
    if ( substr_count( $commentdata['comment_content'], 'http' ) > 2 ) {
        wp_die( 'Too many links. Your comment looks like spam!' );
    }

    // 2. Block if user agent is empty
    if ( empty( $_SERVER['HTTP_USER_AGENT'] ) ) {
        wp_die( 'Invalid comment. Please try again.' );
    }

    // 3. Block comments containing banned words
    $banned_words = array( 'viagra', 'casino', 'loan', 'hack', 'porn' );
    foreach ( $banned_words as $word ) {
        if ( stripos( $commentdata['comment_content'], $word ) !== false ) {
            wp_die( 'Your comment contains restricted words.' );
        }
    }

    return $commentdata;
}
add_filter( 'preprocess_comment', 'rcwebkit_block_spam_comments' );