Computer viruses generally trick hosts or other types of computers into reproducing copies of the invading organism. They spread from computer to computer through electronic bulletin boards, telecommunication systems and shared floppy disks. Viruses are created by human programmers, for fun or malice, but once they begin to spread they take on a life of their own, creating disruption, dismay and paranoia in their wake.
If the virus is found in any of the PC's that PC should immediately be isolated. The virus can be removed by giving an antidote by studying the virus. The machine should be put into use only after the virus is eliminated.
Viruses and such
A Virus is defined as a program inserted into another program. It gets activated by its host program. It replicates itself and spreads to others through floppy transfer. A virus infects data or program every time the user runs the infected program and the virus takes advantages and replicates itself.
There are two types of computer viruses 'parasitic' and 'boot' virus.
A Parasitic virus attaches itself to other programs and is activated when the host program is executed. It tries to get attached to more programs so that chances of getting activated is more. It spreads to other computers when the affected programs are copied. 'Jerusalem' and 'Datacrime' are parasitic viruses.
A Boot virus is designed to enter the boot sector of a floppy disc. It works by replacing the first sector on the disc with part of itself. It hides the rest of itself elsewhere on the disc, with a copy of the first sector. The virus is loaded by the computers built-in start-up program when the machine is switched on. The virus loads, installs itself, hides the rest of itself and then loads the original program. On a hard disc, virus can occupy DOS boot sector or master boot sector.
Some Reported Viruses
C-Brain: Amjad and Basit, two pakistani brothers, developed this software in January 1986 to discourage people from buying illegal software at throwaway prices. This was the most famous virus ever found and has a record of damaging few millions of personal computers. This is designed to stay in the boot sector of the disc or near zero sector. The virus enters the machine memory once the PC is booted with the infected floppy.
Macmag: This virus attacked Apple Macintosh computers only. Not much damage is reported because of this virus. This was not noticed on any IBM compatible PCs. It displayed a message of peace on the monitor and killed itself.
Cascade: This virus attacked IBM PCs and compatibles. The letters on the screen could be seen dropping vertically down to the bottom of screen after the virus picked them off in alphabetical order. This is a sort of parasitic virus. It attaches itself to other programs and gets activated when the host program is executed. It gets copied to other PCs when the programs are copied.
Jerusalem: Found in 1987 at Hebrew University, Jerusalem, this virus was designed to activate only on Friday, January 13 and delete all the files executed on that day. This infects the COM and EXE files. This is similar to Cascade virus in that it is parasitic in nature. This virus attaches itself to COM and EXE files to damage the data.
Daracrime/Columbus or October the 13th virus: This virus is similar to Jerusalem and was programmed to attack on October 13, 1989. Track zero of computer hard disk is destroyed and the contents of discs are rendered unreadable. This virus enters COM and EXE files and damages the hard disk. An antidote called 'Vchecker' was developed by the American Computer Society. Fortunately the virus was located in March 1989 itself and the damage reported after October 13 was minimal.
Bomb: This is also know as 'Logic Bomb' and 'Time Bomb'. An event triggered routine in a program that causes a program to crash is defined as a 'bomb'. Generally, 'bomb' is a software inserted in a program by a person working in the company.
Examples Of Computer Viruses
Every day new computer viruses are created to annoy us and to wreak havoc on our computer systems. Below are ten viruses currently cited as being the most prevalent in terms of being seen the most or in their ability to potentially cause damage. New viruses are created daily. This is by no means an all inclusive list. The best thing you can do is to remain vigilant, keep your anti-virus software updated, and stay aware of the current computer virus threats.
A Trojan horse that attempts to download remote files. It will inject a .dll file into the EXPLORER.EXE process causing system instability.
A mass-mailing worm that lowers security settings. It can delete security-related registry sub keys and may block access to security-related websites.
A Trojan horse that allows the compromised computer to be used as a covert proxy and which may degrade network performance.
A mass-mailing worm which spreads by emailing itself to addresses produced from files on the local drives.
A mass-mailing worm and IRC backdoor Trojan for the Windows platform. Messages sent by this worm will have the subject chosen randomly from a list including titles such as: Notice of account limitation, Email Account Suspension, Security measures, Members Support, Important Notification.
A mass-mailing worm and IRC backdoor Trojan similar in nature to W32-Mytob-GH. W32/Mytob-EX runs continuously in the background, providing a backdoor server which allows a remote intruder to gain access and control over the computer via IRC channels. This virus spreads by sending itself to email attachments harvested from your email addresses.
Virus: W32/Mytob-AS, Mytob-BE, Mytob-C, and Mytob-ER
This family of worm variations possesses similar characteristics in terms of what they can do. They are mass-mailing worms with backdoor functionality that can be controlled through the Internet Relay Chat (IRC) network. Additionally, they can spread through email and through various operating system vulnerabilities such as the LSASS (MS04-011).
A mass mailing worm and a peer-to-peer worm which copies itself to the Windows system folder with the filename Norton Update.exe. It can then create a number of files in the Windows system folder with filenames consisting of 8 random characters and a DLL extension. W32/Zafi-D copies itself to folders with names containing share, upload, or music as ICQ 2005a new!.exe or winamp 5.7 new!.exe. W32/Zafi-D will also display a fake error message box with the caption "CRC: 04F6Bh" and the text "Error in packed file!".
A mass-mailing worm with IRC backdoor functionality which can also infect computers vulnerable to the LSASS (MS04-011) exploit.
A peer-to-peer (P2P) and email worm that will copy itself to the Windows system folder as a randomly named EXE file. This worm will test for the presence of an internet connection by attempting to connect to www.google.com or www.microsoft.com. A bilingual, worm with an attached Hungarian political text message box which translates to ?We demand that the government accommodates the homeless, tightens up the penal code and VOTES FOR THE DEATH PENALTY to cut down the increasing crime. Jun. 2004, P'cs (SNAF Team)?
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