Information system is vulnerable to destruction, error and abuse because it is one type of digital data. Digital data are vulnerable to destruction, misuse, error, fraud, and hardware or software failures. When large amounts of data are stored in electronic form, they are vulnerable to many more kinds of threats than when they existed in manual form. The Internet is designed to be an open system and makes internal corporate systems more vulnerable to actions from outsiders. It also are more vulnerable because it virtually open to anyone. Hackers can unleash denial-of-service (DoS) attacks or penetrate corporate networks, causing serious system disruptions. Wi-Fi networks also can easily be penetrated by intruders using sniffer programs to obtain an address to access the resources of the network. Computer viruses and worms can disable systems and Web sites. Software presents problems because software bugs may be impossible to eliminate and because software vulnerabilities can be exploited by hackers and malicious software. Therefore, end users often introduce errors.