Popular Viruses and Worm Programmes

  • 2000
           May : The VBS/Loveletter ('ILOVEYOU') worm appeard. As of 2004 this is the most costly virus to business, causing upwards of 10 billion dollars in damage.
  • 2001
            January : A worm strikingly similar to the Morris worm, names the Ramen worm infected only Red Hat Linux machines running version 6.2 and 7.
             July 13 : The Code Red worm attacking Microsoft Internet Information Services.
             October 26 : The Klez worm is first identified. 
  • 2003
             January 24 : The SQL slammer worm also known as the Sapphire worm, attacked vulnerabilities in Microsoft SQL Server and causes widespread problems on the internet.
             August 12 : The Blaster worm, also known as the Lovesan worm, spread rapidly by exploiting Microsoft Windows computers.
  • 2004
             January : MyDoom emerges, and currently holds the record for the fastest-spreading mass mailer worm.

             December : Santy, the first known "webworm" is launched. It infected around 40000 sites before Google filtered the search query by the worm.
  • 2005
           August 16 : The Zotob worm and several variations of malware exploiting the vulnerability described in MS05-039 are discovered. The effect was overblown because several United States media outlets were infected.
  • 2006
              January 20 : The Nyxem work discovered. It spread by mass-mailing. It attempts to certain types, such as Microsoft Office files.
               February 16 : Discovery of the first-ever virus for Mac OS X, a low-threat worm known as OSX/Leap-A or OSX/Oompa-A, is announced.
  • 2007
               January 7 :  A worm generated by hackers of the popular website MySpace was discovered by many users on the site.

Components of a Virus

A virus comprises of four general components.
  • The replicator (or Engine) : Replicates the virus.
  • The safeguard : Prevents the detection and the removal of the virus.
  • The trigger monitor : Monitors for a specific condition to deliver payload. These specific conditions may be the arrival of a particular date, time, keyboard stroke, etc.
  • The payload : the action it does apart from propagation. This action may be an amusing or malicious action resulting in distraction from the current work or destruction of data.

Computer Viruses

Some of the main reasons for writing viruses are;
  • Hacking.
  • To prevent copying software.
  • Revenge - Employees may plant "Time Bombs" in programs.
  • Fraud - Viruses may allow access to an otherwise secure system.
  • Political and terrorist motives.
  • Commercial sabotage - Damage the reputation of a competitor.
  • Warfare - Incorporate a virus to an enemy's computer.

Viruses can be transmitted from one system to another through various media types such as;
  • Floppy disks.
  • Tape backups.
  • Internet.
  • Software.
Some of the symptoms that a computer will show up when infected with a virus are listed below.
  • Programs take long time to lead than normal.
  • The floppy disk drive or hard drive runs when you are not using it.
  • New files keep appearing on the system and you do not know where they come from.
  • Strange sound or beeping noises come from the computer or keyboard.
  • Strange graphics are displayed on your computer monitor.
  • Files have strange names you do not recognize.
  • Unable to access the hard drive when booting from the floppy drive.
  • Program sizes keep changing.
  • Conventional memory is less than it used to be and you cannot explain it.


Network Protocols

           A network protocol is "an agreement on how to converse". The four most commonly used network protocols are TCP/IP, IPX/SPX, X.25 and SNA. Each protocol performs essentially the same functions, but each protocol is incompatible with other unless there is a special device to translate between them.

TCP/IP Network Addressing

              TCP/IP protocol uses 3 different types of addressing to move data between computers: Physical, Logical and Port addresses. The physical addresses (MAC addresses) are utilized to move data within a single LAN, logical addresses (IP addresses) are used to move data from one LAN to another LAN across the network and the port address is used to transmit data to the intended application.

              MAC addresses burned into hardware. IP address is a 32-bit value. This means that there are fore billion different IP address possibilities. IP addresses may be sent in software and are thus flexible. An IP address contains the address of the device itself as well as the address of the network on which the device is located. Therefore, if a device is moved from one network to a different network, the IP address of the device must be changed. IP addresses are hierarchical addresses like phone numbers and zip codes. They provide a better way to organize computer addresses like social security numbers. 

              The International Network Information Center (InterNIC) assigns to companies blocks of IP addresses based on the size of their networks.

How to Determine Your IP Address?

                                                     Go to the Start menu and select Run... Then type "cmd" in the box and click OK. Then type "ipconfig" in the command prompt and press Enter.

Backbone Network Components

         A backbone network is a network that connects many networks in a single site. There are many backbone network components.

  • Router - A router is a special device that enables the connection of two or more networks so that the computers in different networks can communicate with each other. A router may be a special device, a computer with several network interface cards or a special network module in a computer or other network device. Routers also allow a network to be segmented into smaller logical networks or subnets.

  • Bridge - A Bridge is an interface that enables similar networks to communicate.

  • Gateway - A Gateway is an interface that enables dissimilar networks to communicate. 


Data Transmission Types

       In a network data can be transmitted in two different ways, serial transmission and in parallel transmission.
  • Serial Data Transmission - Bits are transmitted sequentially, one after the other.
  • Parallel Data Transmission - Bits are transmitted through separate channels simultaneously.
     The standard unit of measure used to specify the speed of the data flow through a network is bits per second (bps).

Network Interface Card (NIC)

 A network Interface Card provides the physical connection between the computer and a network cable and enables access to a network. Most modern computers come with NIC cards pre-installed, and ready to be connected to networks.

 Types of Networks

             There are two primary types of networks.
  • Local Area Networks (LAN) - LAN is a communication network that serves users within a confined geographical area. Private parties generally own LANs and their effective range is limited.
  • Wide Area Network (WAN) - WAN is a communications network that has no geographical limit. A WAN may span hundreds or thousands of miles. In general, a WAN is made up of a number of interconnected LANs. WANs can use either analog (telephone lines) or digital signals or a combination of both. WANs may be privately owned by large organizations or may be public.
  • Local Area Networks (LAN) - Local area networks are two types: client server and peer- to-peer. 
            - Client Sever
                                   A Client server LAN consists of devices that provide services called servers, and devices that request services from servers, called clients. Typically servers are the devices that manage shared devices such as printers.

           - Pear-to-Peer Networks 
                                         In a peer-to-peer LAN there is no server, instead all devices communicate directly with each other. Peer-to-Peer networks are also called work groups. In a peer-to-peer network there is no hierarchy among the computers. Typically the number of computers in a peer-to-peer network would be less than 10. All the computers in the network are treated equal and are referred to s peers. Each computer may function as a client and a sever and there is no central administrator to manage the entire network. The users at each computer determine what data on his computer should be shared with the other peers.


Communication Media

           The communication media is the matter or substance that carries the voice or data. Many different types of transmission media are currently in use. All these different media types can be grouped into two categories: Guided media and Radiated media.

Guided Media

          The guided media are those in which the data flows through physical media.
  • Twisted-pair Wire - A twisted-pair wire consists of two insulated copper wires, twisted around each other and covered in another layer of plastic insulation.
  • Coaxial Cable - A coaxial cable consists of insulated copper wire wrapped in a metal shield, which is then wrapped in an outer external cover. Often many coaxial cables are  bundled together.
  • Fiber-Optical Cable - Consists of hundreds of thin glass wires that transmit pulsation beams of light.

Radiated Media

             And the radiated media are those in which the data is broadcast through the air.
  • Radio Transmission - Radio transmission use the same basic principle as standard radio transmission. When using radio transmission each device/computer on the network should equipped with a radio transmitter/receiver on a specific frequency that does not interfere with commercial radio stations. The transmitters are very low power and are designed typically to transmit a signal to a very short distance, typically up to 500 feet.
  • Infrared Transmission - Infrared transmission uses low-frequency light wave, below the visible spectrum, to transmit data through the air. Infrared transmitters are seldom uses to transmit data to and from portable or handheld computers.
  • Microwave Transmission - Microwave is a high-frequency beam with short wave length. Microwave can be transmitted over a direct line-of sight path between any two points. This transmission medium is typically used for long-distance data/voice transmission.
  • Satellite Transmission - In satellite transmission, singles are transmitted to a satellite 500 to 22,000 miles in space. One disadvantage of satellite transmission is the delay that occurs in transmission, which is known as the propagation delay.

Network Topologies

           Networks can be laid out in a number of different ways. The physical layout of a network is called its topology. The basic network topologies are Star, Ring, Bus. These basic topologies can be combined in a variety of ways to build complex hybrid network topologies.

Star Topology

           In a star network all computers and other communications devices are connected to a central point such as a hub, file sever or a host computer.

Ring Topology

            In a ring network all communications devices are connected in a continuous ring. Messages are passed around the ring until they reach the right destination.

Bus Topology

           In a bus network communications devices are connected to a common channel. There is no central computer and the communications devices transmit message to the other devices.

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