The computer programs that affect the computer programs and computer system is called computer virus. In other word computer virus is a man-made malicious software which is executed or loaded in user’s computer. Computer virus never occurs naturally. After execution, it disrupts the normal functioning of computer or software where the virus was executed. It can do verities of things ranging from editing, changing or deleting the files or programs, displaying unwanted popups and messages, causing the system to malfunction.
Computer virus can hide in host programs, replicate themselves and
even can spreads from one infected program to another program or software. The aim of developing a computer virus is to attack network elements and
vulnerable systems, take control of administrators, and steal sensitive data from users.
John von Neumann, who lectured at the University of Illinois on the “Theory and Organization
of Complicated Automata” published the first academic dissertation on the theory of self-replicating machine programs in 1949. However, the term “computer virus” was described in 1983 only by Fred Cohen.
There are many reasons for creating computer viruses. Some of the reasons may be to stop piracy, to earn money, to steal, misuse and destroy data and information and for entrainment purpose.
During early days of computer era, computer viruses spread through storage devices like floppy disk. Nowadays, it can be transferred from internet. The other methods for transferring of computer virus is from the email attachments either in the form of rich text e-mail or attached applications. When infected files or programs are activated to the normal computer, the viruses then start replicating and try to infect, harm other files, programs, software along with operating system.
There are different types of computer viruses. Some of the viruses are:
- BOOT SECTOR VIRUS:
Examples: Elk Cloner, Monkey, C-brain, NYB, Disk killer, form, Stone etc.
- BROWSER HIJACKER
Examples : Ask toolbar, Coupon saver, Go save etc.
- DIRECT ACTION
Examples: Vienna, Win 64.Rugrat etc.
- FILE INFECTOR
Examples: Ambulance virus, Die heart virus etc.
- Macro Virus
Examples: Loveletter, Marker, Melissa etc.
- MULTIPARTITE VIRUS
Examples: Junkie virus, Flip virus, Invader virus, Tequila virus
- Polymorphic VIRUS
Examples: VIRLOCK , BAGLE or UPolyX, URSNIF, VOBFUS etc.
- RESIDENT VIRUS
Examples: Onehalf virus, Jerusalem virus, Magistr virus
- WEB SCRIPTING VIRUS
Examples: HTML.Redlif.A, ILOVEYOU, DDoS etc.
Protection methods from computer viruses:
- Do not click on the link that looks suspicious and do not download unsafe programs.
- Before opening email attachments, make sure that the email is not doubtful and free from virus.
- Install reliable antivirus application, defender and latest security patch programs.
- Automatic scan computers in daily or weekly basis.
- Avoid cracked and pirated software.
- Install anti-spyware, anti-malware and firewall if necessary.