Computer Networking: Internet Protocols in Action

Chapter 6.3. System Vulnerabilities

INTRODUCTION

Computer systems are vulnerable to a wide variety of attacks from malicious software such as computer viruses or worms. Malicious software is generally referred to as malware. Malware varies significantly in its purpose and method of attack.

Malware often enters a computer system by tricking legitimate users into downloading it or otherwise introducing it into the system. Users may execute malware when they open an e-mail attachment, download a file from a web site or use a floppy disk containing infected files. Once executed, the malicious program typically runs with the legitimate user's full rights and privileges. For example, any file the user could delete, the malware can delete; any network connection the user could make, malware can make; any program the user could install, malware can install.

What do malware programs do with the power they acquire? Some programs simply want to irritate, perhaps by displaying a message to let the user know they've been attacked. However, other programs seek to destroy the system, perhaps by deleting key system files. In both these cases, users can easily detect that they have been attacked.

Some malware programs attempt to accomplish their goals without alerting users. For example, they may search the files on the computer for e-mail addresses or credit card numbers to send over the network to their creators. Others simply lurk unobtrusively but open a back door through which their creators can ...