A computer virus is a computer program that can copy itself and infect a computer without the permission or knowledge of the owner. The term "virus" is also commonly but erroneously used to refer to other types of malware, adware and spyware programs that do not have the reproductive ability. A true virus can only spread from one computer to another (in some form of executable code) when its host is taken to the target computer; for instance because a user sent it over a network or the Internet, or carried it on a removable medium such as a floppy disk, CD, DVD, or USB drive. Viruses can increase their chances of spreading to other computers by infecting files on a network file system or a file system that is accessed by another computer.[1][2]
Viruses are sometimes confused with computer worms and Trojan horses, which are technically different. A worm can use security vulnerabilities to spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a program that appears harmless but has a hidden agenda. Worms and Trojans, like viruses, may cause harm to either a computer system's hosted data, functional performance, or networking throughput, when they are executed. Some viruses and other malware have symptoms noticeable to the computer user, but most are surreptitious. This makes it hard for the average user to notice, find and disable and is why specialist anti-virus programs are now commonplace.
Most personal computers are now connected to the Internet and to local area networks, facilitating the spread of malicious code. Today's viruses may also take advantage of network services such as the World Wide Web, e-mail, Instant Messaging and file sharing systems to spread, blurring the line between viruses and worms. Furthermore, some sources use an alternative terminology in which a virus is any form of self-replicating malware.
THE FIRST COMPUTER VIRUShe Creeper virus was first detected on ARPANET, the forerunner of the Internet in the early 1970s.[3] Creeper was an experimental self-replicating program written by Bob Thomas at BBN in 1971.[4] Creeper used the ARPANET to infect DEC PDP-10 computers running the TENEX operating system. Creeper gained access via the ARPANET and copied itself to the remote system where the message, "I'm the creeper, catch me if you can!" was displayed. The Reaper program was created to delete Creeper.[5]
A common misconception is that a program called "Rother J" was the first computer virus to appear "in the wild" — that is, outside the single computer or lab where it was created, but that claim is false. See the Timeline of notable computer viruses and worms for other earlier viruses. It was, however, the first virus to infect computers "in the home." Written in 1982 by Richard Skrenta, it attached itself to the Apple DOS 3.3 operating system and spread via floppy disk.[6] This virus was originally a joke, created by a high school student. It was injected in a game on a floppy disk. On its 50th use the Elk Cloner virus would be activated, infecting the computer and displaying a short poem beginning "Elk Cloner: The program with a personality." With time VIRUS’s became more and more complicated and nowadays they tend to be very compact and highly target specific
COUPLE OF MOST COMMON VIRUS CURRENTLY ON THE GOMEDIACONTROL VIRUS – This code usually breaks into a system via email attachments .The most interesting about this virus is that it can slip past even the best antivirus software’s available in today’s market .Once in a system it changes the extension of all media files like .avi .flv. asf .wmv to .jpeg which is the extension for an image file .The result is that whenever the user tries to play a song or a video, instead of media software’s like windows media player, image opening software like windows fax viewer starts and naturally it cant play the media files so it displays an error. One way of tackling this problem is again renaming the jpeg extension to the original extensions but there are so many media files present in any average PC it is impossible to remember each and every of their original extensions .If the original extension is not given the file becomes useless forever
AUTORUN VIRUS – This virus sort of locks the drives of the PC.on the infected PC if the user tries to open the D drive (for that matter any drive) then instead to opening up a messege is displayed “Windows cannot open this file. To open this file windows needs to know the program which created it ” .Thus the drives are treated as unknown files which causes a great deal of problem in working with them.
SYMPTOMS OF A VIRUS INFECTED COMPUTER
1. Abnormal program behavior in windows like being unable to view hidden files, unable to open hard disk, wrong disk volume information ,frequent errors
2. System slowdown ,PC taking too much time in loading startup items
3. Blue screens of death which are popularly called BSOD
4. Errors like
“svchost.exe - Application Error The exception unknown software exception (0xc0000409) occurred in the application at location 0x5b86a3c0.”
“unable to read memory referenced …”
and frequent “ this program has performed an illegal operation” messeges
5. And finally sudden system crashes
THE ABOVE ARE SYMPTOMS ONLY .THE ABOVE SIGNS DON’T GUARANTEE THAT A VIRUS IS PRESENT IN THE PC ,THESE CAN BE DUE TO HARDWARE ISSUES ,SOFTWARE CONFLICTS .HOWEVER THERE IS A HIGH PROBABILITY THAT THE SYSTEM IS INFECTED
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