A computer virus is a type of malicious software that, when executed, replicates itself by modifying other computer programs and inserting its own code. All Viruses are man made. People develop virus for their protection but some people use it for destroy others.

1) The Morris worm

• First computer worms distributed via internet.
• Type : Internet worm
• Creator: Robert Morris, Jr.
• Date Discovered: 1988.11.02
• Place of Origin : Cornell, MIT*
• Source Language: C
• Platform : BSD, SunOS
• Reported Costs : $1 million

2) The Concept virus

• Type :Word macro virus
• Date Discovered: 1995.07
• Source Language: Visual Basic
• Platform: MS Word
• File Type(s): .doc
• Infection Length :5 macro modules
• Reported Costs:

3) CIH

• Type: File virus
• Creator: Chen Ing Hau
• Date Discovered: 1998.06.25
• Place of Origin :Taipei, Taiwan
• Source Language: Assembly
• Platform: Windows 9x
• File Type(s): .exe
• Infection Length: 1,000 Bytes
• Reported Costs :$250,000,000

There are many more viruses that harms your PC.