That is precisely the reason for the legal banners. It was once common for the login process on UNIX systems to have a phrase similar to "Welcome to System XXXX". That was interpreted in court as tacit permission access the system. There was a mad scramble to update every system in the company to emit the legal prohibition banners in a manner visible before an attempt to login occurs. I had to modify the UNIX systems on 12 UNISYS mainframes in August 1984 to comply with company security. My colleagues with the 3B20S systems had many more systems to update.