Device Invisible to 98% of Malicious Actors

The author has developed an operating system for a controller that supports various ports such as Telnet, SSH, FTP, HTTP, HTTPS, etc., without third-party code. To reduce malicious connection attempts, they implemented Greylisting at the TCP level, ignoring the first connection attempts (SYN) and only responding to repeated attempts within a certain time frame. This method has significantly reduced malicious activity, making the device almost invisible to malicious actors.