IANAL but I would assume computer fraud and abuse act:
(5)(a)knowingly causes the transmission of a program, information, code, or command, and as a result of such conduct, intentionally causes damage without authorization, to a protected computer;
In the cases cited under the CFAA (such as https://scholar.google.com/scholar_case?case=124545279862007...) it seems the employee deleted data and private info. In this case, no data was deleted or other computing property damaged it just became unreachable.
Screen savers?
Also login / lock screens are essentially just screen savers