We have all heard of the dangers of the Internet and Cyberspace. Although some of these have been greatly exaggerated, it does not alter the fact that a computer connected to the Internet is open to very real attacks. Unfortunately, there are psychotics and criminals (possibly the same thing) who feel compelled to make life difficult for others. Some of these know about computers and how to access files remotely. These are called crackers. To keep them out of our systems we need to use a strong firewall.
Here are the main dangers:
Unauthorized applications can be delivered to your computer and be executed without your knowledge or control (for example, ActiveX or Java applets embedded in a web page you are browsing). These programs can perform any operation on your computer, including transferring files containing your private information to other computers or simply erasing all the files on your system.
If your system is incorrectly configured (NetBIOS or Remote Procedure Call , for example, are installed by Windows by default) other computers can access your files directly without someone having to surreptitiously load special software on your computer.
Some information (in the form of cookies or referrers ) can be placed on your computer, so advertisers and others can track the sites you visit and what your interests are.
Trojan horses can be placed on your computer. Trojans are programs used by crackers that open the door to your private information, such as passwords, banking data and credit card numbers. One of the fundamental differences between a Trojan and a virus is a virus on your computer executes autonomously, whereas a Trojan horse is constructed to be used directly by the intruder who sent it.
Unnecessary data in the form of banners and other advertisements use up your bandwidth. Although these objects cannot directly access or damage the data on your computer, they can significantly slow your connection, especially on a dial-up.
Spyware are programs that gather information about you and your interests. Some of America's on-line corporations are placing this software on home computers without the owner's knowledge or permission.