The types of countermeasure to threats on computer systems range from physical controls to administrative procedures. Despite the range of computer-based controls that are available, it is worth noting that, generally, the security of a DBMS is only as good as that of the operating system, owing to their close association. Representation of a typical multiuser computer environment is shown in Figure 19.2. In this section we focus on the following computer-based security controls for a multi-user environment (some of which may not be available in the PC environment):