So if you use a version of Windows that is not updated and has a backdoor, is that fair game for "hackers" as well? It is "publicly accessible" for all intents

So if you use a version of Windows that is not updated and has a backdoor, is that fair game for "hackers" as well? It is "publicly accessible" for all intents and purposes. When does it become fair game? In the first day? 100th day? after 2 years?