List and describe the most common threats against contemporary information systems.

1.  The multi-tier client/server computing environment: The vulnerabilities exist at each layer and in the communication between the layers. The user often unauthorized access and introduce errors.
2.   The communications lines: The common threats are tapping, sniffing, message alteration, theft and fraud and radiation.
3. The Corporate Servers: The most common threats are hacking, viruses and worms, theft and fraud, vandalism and denial-of-service attacks.
4.   The Corporate Systems: The most common threats are theft of data, copying data, alteration of data, hardware failure and software failure.