Time-sharing - is the sharing of a computing resource among many users by means of multiprogramming and multi-tasking.
Using system resources (CPU, disk space) without proper accounting – This is one of the problems occurred when you use a time-sharing environment.
Causing the printer to mix output by sending data while some other user's file is printing - This is one of the problems occurred when you use a time-sharing environment.
Can we ensure the same degree of security in a time-share machine as we have in a dedicated machine?
No, because developing a system that supported multiple users at the same time was a completely different concept. The user machine is defined by the combination of the time-sharing hardware running in user mode and the software which controls input-output. If the hardware is arranged in such a way that calls on the system have the same form as the hardware instructions of the machine then the distinction becomes irrelevant to the user; he simply programs a machine with an unusual and powerful instruction set which relieves him of many of the problems of conventional machine-language programming.