15. Describe the role of the following in promoting information system security. (a) Firewall (b) Antivirus software (c) Digital certificates (d) Data encryption 16. (a) If you were developing a business continuity plan for your company, where would you start? What aspects of the business would the plan address? (b) Explain the different types of decisions. (c) Describe the different levels of decision making. 17. (a) Describe the various stages in decision making. (b) Distinguish between an unstructured, semi-structured and structured decision. (c) Describe the purpose of an information systems plan.