Is it legal for one of their computer systems to access mine without my consent, even if publicly routable via the internet? If I found an open port on a gover

Is it legal for one of their computer systems to access mine without my consent, even if publicly routable via the internet? If I found an open port on a government computer it is still illegal for me to access that isn't it? Is the difference that this is port 80/443 and happens to serve HTTP requests something that has been described in law or court?