Add this line $wpdb->query("DELETE FROM `".$wpdb->prefix."adrotate_tracker` WHERE `ipaddress` ='unknown';"); Function now looks like: /*------------------------------------------------------------- Name: adrotate_clean_trackerdata Purpose: Removes old trackerdata Receive: -none- Return: -none- Since: 2.0 -------------------------------------------------------------*/ function adrotate_clean_trackerdata() { global $wpdb; $removeme = current_time('timestamp') - 86400; $wpdb->query("DELETE FROM `".$wpdb->prefix."adrotate_tracker` WHERE `timer` < ".$removeme." AND `ipaddress` > 0;"); $wpdb->query("DELETE FROM `".$wpdb->prefix."adrotate_tracker` WHERE `ipaddress` ='unknown';"); }