What are Computer Viruses and How do they Spread?

• Through removable media like floppy disks, CD's, DVD's, Flash memory pens etc
• Through the computer network (LAN, WAN, etc...) via its various services like file sharing systems
• Internet via Email, web services and other files sharing services in chat and IM.
• It can infect an entire network that is connected to the internet.

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• A program virus is active only when an infected (program) file is run. This virus then resides in the memory of the computer and copies it self to every other program that is being run. In case an infected program file is copied to another computer then the virus spreads the same way on that computer as well.
• Macro viruses become active only when the application program file is opened. This then infects all the other documents that the application program runs. This happens only when the application program can run macros.
• Email viruses spread through emails. This is usually when you open a spam or a virus file unwittingly
• A worm uses security lapses on your system or network. It can only infect computers or networks that do not have proper security.
• A Trojan horse can cause damage and is again downloaded unknowingly along with other downloads from the internet.

History of Viruses

• Theories for self-replicating programs were present long back and are as early as 1946.
• The earliest viruses were found on Apple II operating system. It spread through a pirated computer game
• The word virus was coined somewhere in 1983 by Len Adleman
• Brain the first virus is said to have originated in Pakistan and affected MS-DOS PC's. This was way back in 1986
• PC-Write a Trojan was also developed in the same year as brain
• Stoned a boot sector virus infecting master boot records was noticed in 1987
• The year 1988 proved very eventful as the first antivirus for brain had been developed. But the negative side was the virus Jerusalem and the "internet worm" that crashed 5000 computers.
• Antivirus research continues and IBM released its commercial product in 1989. The same year the Dark Avenger virus appeared.
• Bulletin boards became common to share information for virus programmers.
• Symantec launches Norton Antivirus in 1990.
• 1991 saw the arrival of polymorphic virus that changed its code/appearance with each new infection making it difficult for antivirus scanners. Tequila is the name of this first polymorphic virus
• irus creation kits were developed in the same year (1991) and this saw an increase in the number of virus attacks.
• Keeping track of viruses become difficult now since by 1992 the number of viruses have grown to 1300 in number.
• March 6th 1992 a scare of Michelangelo virus results in around 10,000 computers crashing.
• An email hoax scares everyone in 1994. Called the Good Times; it warns of a erasure of the entire hard disk. This year also saw the first prosecution of a virus (pathogen) writer.
• Microsoft WordBasic program is affected by the first macro virus in the year 1995. This starts a new genre of viruses called macro viruses.
• Other viruses worth mentioning are :
• StrangeBrew affecting Java files
• W97/Melissa a macro affecting outlook and spreading through emails
• Chernobyl virus
• Tristate affecting Word, Excel and power point files
• Bubble boy
• Love bug/I love you virus
• W97M.Resume.A
• Stages
• Liberty which affects Palm PDA
• Anna Kournikova Virus
• Home Page virus
• Home Page virus
• Code Red worms which affected around 700,000 computers
• W32/Sircam
• W32/Nimda worm
• Win32.Badtrans.B, and other variants like Win32.Nimda.A, VBS.VBSWG.Generic, Win32.Goner.A
• Klezworm
• Bugbear
• Sobig
• Blaster
• My Doom

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