01 February 2011

How Computer Viruses Work

A computer virus is a program that reproduces by attaching itself to another program or document. Similar to a biological virus, the virus has a code which is executed when the infected program is run.
This is the general way most viruses work:
  • When an infected program or file is opened, the computer virus attached to it is automatically activated.
  • The virus modifies a computer program’s code so when a user starts the program, the virus code runs instead of the normal code.
  • The moment the virus code becomes activated, the computer will then be under its full control.
  • The virus aims to replicate and spread. Thus, it naturally looks for prospective targets to infect.
More sophisticated virus types now proliferate as a product of its authors’ creativity. Below are some of their tricks:
  • Polymorphing: There are types of virus which can change its appearance and size. Many simple virus scanners then can hardly detect an infected file since it only monitors and searches a computer virus based on predefined patterns.
  • Stealth: This kind of virus actively hides the changes it has made to the hard disk so it looks as if it has not infected the system. For example, a file infector may stay memory-resident and wrongly report the size of infected files so they don’t appear infected. Boot sector viruses can trap attempts to read the boot sector and return forged data.
  • Disassembly Protection: There are many programming tricks that can be used to design viruses in such a way that it cannot be detected and combated.
An anti-virus software is a must-have protection for anyone who has or is working with computers. The Internet has made viruses easier to spread, and since most rely on computers everyday, it is vital that they operate properly.
Here are some useful anti-virus software resources:
Source: http://smart.com.ph/SmartSchools/SmartTools/HowComputerVirusesWork.htm

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