Fundamentals of Computer Systems

 Let us first revisit the concept of network. A computer network is simply a system of interconnected computers. That is used every day to conduct transactions and communications among businesses, government agencies and individuals. The networks consist of "nodes", which are "client" terminals (individual user PCs), and one or more "servers" and/or "host" computers. They are linked by communication systems, some of which might be private, such as within a company and others which might be open to public access. The obvious example of a network system that is open to public access is the Internet, but many private networks also utilize publiclyaccessible communications. Today, most companies' host computers which can be accessed by their employees whether in their offices over a private communications network, or from their homes or hotel rooms while on the road through normal telephone lines. Hence, security plays a crucial role in that. Now...

 3.0 INTRODUCTION The previous two units discussed about the fundamentals of information as well as network security issues which lead to different kinds of problem: attacks, theft of essential information and software vulnerabilities. In this unit, we shall learn about how to build a secure network. We shall also learn about the various parameters which must be considered for network security. There can be various security issues involved in small and medium sized businesses which require utmost attention for creating the secure network. Then we shall be covering different kind of tools available for network security, critical elements of network security like Firewall, password mechanisms, encryption, authentication & integrity etc. Lastly, we shall study about some secure network devices like secure modems. Let’s first study the basics of network and network security. 3.1 OBJECTIVES After going through this unit, you should be able to:· understand the scope of network securi...

 Social Engineering is the name given to a category of security attacks in which someone manipulates others into revealing information that can be used to steal data access to systems, access to cellular phones , money or even your own identity. The complexity of such attacks may vary from very low to high. Gaining access to information over the phone or over website that one may visit has added new dimensions to the field of social engineering. Social engineering is basically the acquisition of sensitive information or inappropriate access privileges by an outsider based upon the building of an  inappropriate trust relationship with the insiders. The “outsider” does not always refer to a person who is not an employee of the company or is stranger to you; an employee who tries to tamper the company policies is also a social engineer. The goal of social engineering is to trick someone into providing valuable information or access to that information or resource. The social engi...

 Each kind of virus has different goals and objectives as we saw in the case of the previous two. Like a virus, a Trojan horse is a hidden piece of code. Viruses enter in a system secretly where Trojan horse enter by deceiving a user. A user allows or invites a Trojan into the system, believing in it, but actually Trojan horse contain some malicious code to perform some malicious activity. Before a Trojan can attack, it must find a way to entice the victim to copy, download and run it. Since few people would knowingly run a malicious program, Trojan must disguise themselves as other programs that the victim believes to be harmless (such as games, utilities or popular applications). This is not all, besides disguising themselves as harmless programs, Trojan horses can also disguise themselves into a legitimate program, such as Adobe Photoshop or Microsoft Excel. To do this, malicious hackers have created special wrapper or binder programs with names such as Saran Wrap, silk rope whi...

 A worm shares many characteristics with a virus. The most important characteristic is that worm is self replicating too. Worms seek to infect and replicate without targeting and infecting specific files already present on a computer. . The two most common ways a worm can spread are through email and security flaws in computers connected to a network or the Internet. If a virus infects a legitimate file, the virus code can be cleaned out and removed. But this is not the case with worms. Worms generally create and occupy the files that contain their code without using or involving any real data or binary files, the normal cleanup technique for worms is to delete all infected emails or messages that provide their containers. Worms which use email to spread are known as massmailing worms and are typically written in a variant of the Visual Basic programming language. They usually exploit the Microsoft Outlook or Outlook Express emailing programs on Windows. Typically, the worm checks ...

 A virus is a malware that, when executed tries to replicate itself into other executable code. When it succeeds, the code is said to be infected. The infected code when run can infect new code in turn. The virus are self replicating and parasitic. It replicates by being copied or initiating its copying to other program, computer boot sector or document. Viruses can be transmitted as attachments to an email note, downloaded file or be present on a diskette or CD. Some viruses start their effects as soon as their code is executed; other viruses lie dormant unless circumstances cause their code to be executed by the computer. Generally speaking, viruses hide within computer files rather than sitting out in open, in some obvious, visible and separate form. But viruses must be run in order to allow them to proceed with their destruction work. Until this happens they cannot do any harm. This explains why the most effective technique for fending off viruses is to inspect all files and me...

 To understand how a malware infects a system, we go back to the elementary working of a computer. On booting, the system carries out the ROM (Read Only Memory) instructions, the first being the power on Self Test which is followed by the bootstrap process of reading the boot record and loading of the disk operating system. The booting process culminates into the system prompt displayed on the monitor. The infection may begin as soon as a computer system boots from a contaminated disk or executes an infected program. Whatever malwares are present gets activated, which immediately begin to spread throughout the system. Another important aspect that needs mention here is the interrupt mechanism. All input/output activities on a PC are carried out by interrupts. We will try to understand the concept of interrupt with an example. Let us say, a user wishes to save his program and presses on the key board. This is treated as an interrupt. The main memory has specific routines to handle t...