Unit II - Computer Virus & Network Communication

Computer Virus

What is computer virus?

v  It is a parasitic program that infects another legitimate program which is called the host.

v  Computer virus refers to a   program which damages computer systems and/or destroys or erases data files

Important Characteristic of  computer virus is its ability to replicate itself

Computer Virus spreads in the following ways

•      Downloading an infected file to your computer

•      Receiving an infected disk from another user

•      Copying an infected file

What can a virus do?

•      It can annoy their victims rather than cause specific damage. They are described as benign.

•        Causes damage to computer system if permitted to run.

Computer Viruses are programs that are created for the following purposes. They are:

q  Copy themselves to other programs or areas of disk

q  Replicate rapidly and frequently

q  Display information in the screen

q  Modify, Corrupt or destroy selected files

q  Erase the contents of entire disk

q  Lie dormant for a specified time or until a given condition is met and then becomes active

Types of Computer Virus

•      Bimodal, Bipartite or Multipartitie Virus

•      Logical Bombs

•      Time Bombs

•      Boot sector Virus

•      Cluster Viruses

•      Joke Programs

•      Stealth Virus

•      Script Virus

•      Trojan Horses

•      Worm

•      Macro Viruses

•      Script Virus

•      Polymorphic Virus

Bimodal, Bipartite, Multipartite Virus

This typeof virus can infect both files and boot sector of a disk.

Time Bomb

A time bomb is a virus program that performs an activity on a particular date .It hides on a victim’s disk and waits until a specific date before running

Logical Bomb

           A logical bomb is a destructive program that performs an activity when a certain action has occurred. It may be activated by a date, a change to a file or a particular action taken by a user or a program

Worm Virus

A worm is also a destructive program that fills a computer system with self-replicating information. Effective worm copies itself and takes up as much space as possible in the Host’s memory . Worms are commonly spread over Internet .

Boot Sector Virus

      A boot sector virus infects boot sector of computers. During system boot, boot sector virus is loaded into main memory and destroys data stored in hard disk . When the computer is started the virus copies itself into memory where it hides and infects other disks .

  Cluster virus

 This type of virus makes changes to a disk’s file system. If any program is run from the infected disk, the program causes virus to run . This causes illusion that the virus has infected every program on the disk.

Joke Programs

       These are not viruses and do not inflict any damage . Their purpose is to frighten their victims into thinking that a virus has infected and damaged their system. For example a joke program can display a message warning to the user not to touch any keys or the computer’s hard disk will be formatted.

Macro Virus

A macro virus is associated with application software like word and excel. When opening the infected document, macro virus is loaded into main memory and destroys the data stored in hard disk .

Script Virus

Commonly found script viruses are written using the Visual Basic Scripting edition (VBS) and the JavaScript programming languages .

Trojan Horses

Trojan Horse is a destructive program. It usually pretends as computer games or application software. If executed, computer system will be damaged.Trojan Horse usually comes with monitoring tools and key loggers

Polymorphic Virus

This can change itself each time it is copied, making it difficult to isolate .

Stealth Virus

          This virus takes up residence in Computer memory, making it hard to detect.

Antivirus Softwares:

In order to protect our computer systems from the danger of virus infection, we can follow certain precautionary measures as well as some remedial measures. These measures include the use of certain softwares called Antivirus Softwares to protect our files from being infected by computer viruses.

•         Antivirus Software is a software that scans computer memory and disks for known viruses and eradicates them. A good Antivirus Program checks for infected files automatically every time you insert any kind of disk or download a file via network or internet connection . It can also scan email messages and attached files . Sophisticated Virus scanners can also alert you if a web page attempts to load suspicious code onto your PC.

Some of the  Popular Anti virus Programs are :

»          McAfee Antivirus

»        Norton Antivirus

»        Virex

»        PC-cillin

»        Avast .

»        Kaspersky Anitvirus.

Actions to prevent virus infection:

v  Always update your anti-virus software at least weekly.

v  Back up your important files and ensure that they can be restored.

v  Change the computer's boot sequence to always start the PC from its hard drive

v  Don't share Drive C: without a password and without read-only restrictions.

v  Empty floppy drives of diskettes before turning on computers, especially laptops.

v  Forget opening unexpected e-mail attachments, even if they're from friends

v  Get trained on your computer's anti-virus software and use it.

v  Have multiple backups of important files. This lowers the chance that all are infected.

v  Install security updates for your operating system and programs as soon as possible.

v  Jump at the chance to learn more about your computer. This will help you spot viruses.

                                                Network Communication

Communication System:

Process describing transfer of information, data, instructions between one or more systems through some media

   Examples

n  people, computers, cell phones, etc.

n  Computer communication systems

Signals passing through the communication channel can be Digital, or analog

n  Analog signals: continuous electrical waves

n  Digital signals: individual electrical pulses (bits)

Communication Model:

 

Characteristics of Communication:

      must have a Sender and  Receiver

      A protocol is a set of rules which governs the transfer of data between computers. Protocols allow communication between computers and networks.

      Handshaking is used to establish which protocols to use. Handshaking controls the flow of data between computers

      protocols will determine the speed of transmission, error checking method, size of bytes, and whether synchronous or asynchronous

Communication Software:

n  Hypertext Transfer Protocol (HTTP): A client/server application that uses TCP for transport to retrieve HTML pages.

n  Domain Name Service (DNS): A name-to-address translation application that uses both TCP and UDP transport.

n  Telnet: A virtual terminal application that uses TCP for transport.

n  File Transport Protocol (FTP): A file transfer application that uses TCP for transport.

n  Trivial File Transfer Protocol (TFTP): A file transfer application that uses UDP for transport.

n  Network Time Protocol (NTP): An application that synchronizes time with a time source and uses UDP for transport.

n  Border Gateway Protocol (BGP): An exterior gateway routing protocol that uses TCP for transport. BGP is used to exchange routing information for the Internet and is the protocol used between service providers.

Communication Hardware:

Any type of hardware capable of transmitting data, instructions, and information between devices

Examples:

Dial-up modem: uses standard phone lines

ISDN and DSL Modem: Allows digital communication between networks and computers

Cable modem: a modem that transmits and receives data over the cable television (CATV) network

Network interface cards: Adaptor cards residing in the computer to transmit and receive data over the network (NIC) (e.g., Ethernet)

Physical Transmission Media:

A tangible media

n    Examples: Twisted-pair cable, coaxial cable, Fiber-optics, etc.

Twisted-pair cable:

n    One or more twisted wires bundled together (why?)

n    Made of copper

Coax-Cable:

n    Consists of single copper wire surrounded by three layers of insulating and metal materials

n    Typically used for cable TV

Fiber-optics:

n    Strands of glass or plastic used to transmit light

n    Very high capacity, low noise, small size, less suitable to natural disturbances

Networks:

n  Collection of computers and devices connected together

n  Used to transfer information or files, share resources, etc.

n  What is the largest network?

n  Characterized based on their geographical coverage, speed, capacities

n  Networks are categorized based on the following characteristics:

n  Network coverage: LAN, MAN, WAN

n  Network topologies: how the computers are connected together

n  Network technologies

n  Network architecture

LAN:

            Local Area Network is a group of computers connected within a building or a campus (Example: computers located on a single floor or a building or it might link all the computers in a small company. 

MAN:

Metropolitan Area Network – a backbone that connects LANs in a metropolitan area such as a city and handles the bulk of communications activity across that region.  

WAN:

Wide Area Network  covers a large geographical area such as a city or country.  Communication channels include telephone lines, Microwave, satellites, etc.

 Bus Topology :

Star Topology :

Ring Topology :