Without hacking password files or stealing sensitive data, a denial of service hacker simply fires up a program that will generate enough traffic to your site that it denies service to the site's legitimate users.
Not only do these attacks prevent Web sites from serving their customers, depending on the size of the attack they can also slow down the entire Internet. According to Keynote Systems, a firm that measures Internet and Web site performance, during the period of recent Internet DoS attacks the performance of the top 40 Web sites was degraded by 60%.
There are three types of DoS attacks: those that exploit a bug in the TCP/IP implementation, those that exploit a shortcoming in the TCP/IP specification, and brute force attacks that clog up your network with so much useless traffic that no other traffic can get in or out. The Ping of Death and Teardrop attacks both exploit known bugs in TCP/IP implementations. Weaknesses in the TCP/IP specifications leave it open to SYN and Land attacks. Smurf attacks are a type of brute force attack that takes advantage of a feature in the IP specification known as direct broadcast addressing. A User Diagram Protocol (UDP) Flood denial of service attack links two unsuspecting systems and causes them to send a nonstop flood of useless data between the two.
Unauthorized Access, Stolen Data, and Viruses.
Viruses, in spite of the new and more advanced security available, are still a growing problem. Globally, from July 1998 to July 1999, 64% of companies were hit by at least one virus, which was up from 53% the year before. In relation, only 15% of companies reported data theft, 11% reported data and system integrity losses, and 13% reported denial of service attacks. Viruses such as the Melissa and Worm viruses, which infected e-mail systems worldwide, represent the single biggest security concern among businesses. Viruses are often spread by e-mail but can also be planted on a company's network by a hacker who gains unauthorized access.
