Define the type of security attack$/$service in the following cases $[2$ marks$]$ a$.$ An employee breaks into a CEO's office to get a copy of important papers b$.$ An employee sends hundreds of emails per day to another employee using a phony return e$-$mail address c$.$ A server disconnects a client if he$/$she logged into the system for more than two hours d$.$ A customer gives a cheque for $10$$ to buy a book. Later he found the cheque was cashed for $100$$