Computer Science JSS3 Second Term

Week 3

Topic: Computer Virus

What is a Computer Virus?

Computer viruses are small software programs that are designed to spread from one computer to another and to interfere with computer operation. A virus might corrupt or delete data on your computer, use your e-mail program to spread itself to other computers, or even erase everything on your hard disk.

Computer viruses are often spread by attachments in e-mail messages or instant messaging messages. That is why it is essential that you never open e-mail attachments unless you know who it’s from and you are expecting it.

A computer virus is a malware program that, when executed, replicates by inserting copies of itself (possibly modified) into other computer programs, data files, or the boot sector of the hard drive; when this replication succeeds, the affected areas are then said to be “infected”. 

A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. All computer viruses are man-made. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.

Viruses often perform some type of harmful activity on infected hosts, such as stealing hard disk space or CPU time, accessing private information, corrupting data, displaying political or humorous messages on the user’s screen, spamming their contacts, logging their keystrokes, or even rendering the computer useless.

Viruses can be disguised as attachments of funny images, greeting cards, or audio and video files. Computer viruses also spread through downloads on the Internet. They can be hidden in illicit software or other files or programs you might download.

Types of Viruses

There are different types of viruses: 

  1. Boot Sector Virus – targets the boot sector of a hard drive and crucially effects the boot process. Boot sector viruses became popular because of the use of floppy disks to boot a computer. The widespread usage of the Internet and the death of the floppy has made other means of virus transmission more effective.
  2. File Infection Virus – coded viruses that attach themselves to .exe files; compressed files such as zip or drive files.
  3. Multipartite Virus – cross between a file virus and a boot sector virus.These type of viruses spread in many different ways. Their actions vary depending on the OS installed and presence of certain files. They tend to hide in the computer’s memory but do not infect the hard disk.
  4. Network Virus – uniquely created to quickly spread throughout the local area network and generally across the Internet as well. Typically moves within shared resources like drives and folders.
  5. Macro Virus – infects program files that use macros in the program itself, such as word processors. These viruses infect the files created using some applications or programs that contain macros such as doc, pps, xls and mdb. They automatically infect the files with macros and also templates and documents that are contained in the file. They hide in documents shared through e-mail and networks.Macro viruses include:
    • Relax
    • bablas
    • Melissa.A
    • 097M/Y2K
  6. E-mail Virus – generally this is a macro virus which multiplies by sending itself to other contacts in your address book, in hopes they’ll activate the virus as well. This is a virus spread via an email. Such a virus will hide in an email and when the recipient opens the mail.
  7. Memory Resident Viruses – They usually fix themselves inside the computer memory. They get activated every time the OS runs and end up infecting other opened files. They hide in RAM. This type of virus is a permanent which dwells in the RAM memory. From there it can overcome and interrupt all of the operations executed by the system: corrupting files and programs that are opened, closed, copied, renamed etc.Memory Resident Viruses Include:
    • CMJ
    • meve
    • randex
    • mrklunky

How Computer Viruses and Worms can impact you

The Viruses and Worms subclass of malicious software programs includes the following:

  • Email-Worm
  • IM-Worm
  • IRC-Worm
  • Net-Worm
  • P2P-Worm
  • Virus
  • Computer Worms Most known computer worms are spread in one of the following ways:
    • Files sent as email attachments
    • Via a link to a web or FTP resource
    • Via a link sent in an ICQ or IRC message
    • Via P2P (peer-to-peer) file sharing networks
    • Some worms are spread as network packets. These directly penetrate the computer memory, and the worm code is then activated.
  • Computer worms can exploit network configuration errors (for example, to copy themselves onto a fully accessible disk) or exploit loopholes in operating system and application security. Many worms will use more than one method in order to spread copies via networks.

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