Computer viruses


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Computer viruses

  1. 1. History, Classifications and Structure PRESENTED BY : IMRAN AHMED KHAN University of Texas at Tyler
  2. 2.  A computer virus is a computer program that can replicate itself and spread from one computer to another. A program that alters other programs to include a copy of itself A computer program able to infect other programs by modifying them to include a Possibly evolved version of Itself.
  3. 3.  Computer virus is a segment of machine code (typically 200-4000 bytes) Do undesirable things ( damages ) Destructive Software
  4. 4.  Search Search for the Host program. Copy Copy itself into the executable program. Anti-Detection Routines to prevent viruses from being detected. Payload Performs the function(s) for which virus was designed.
  5. 5.  Shell virusesA shell virus is one that forms a “shell” around the original code. In effect, the virus becomes the program, and the original host program becomes an internal subroutine of the viral code. Add-on virusesThey function by appending their code to the host code. The add-on virus then alters the startup information of the program, executing the viral code first. The host code is left almost completely untouched
  6. 6.  Intrusive virusesIntrusive viruses operate by overwriting some or all of the original host code with viral code. The replacement might be selective, as in replacing a subroutine with the virus.
  7. 7.  As soon as user run the host program which is infected. Specific date or time. Examining user keystrokes for a specific sequence. Some random event.
  8. 8. Sample Source Code
  9. 9.  Setting up a test machine Knowledge of all viruses in detail How it infects executable, what to look for to determine that the executable has been infected. Knowledge of anti-detection techniques.
  10. 10.  First generation: SimpleDo Replication only.Detect easily.Cannot Hide itself. Second generation: Self-recognitionSolved one problem in prior generation viruses.Prevent unnecessary growth of infected files.Use of signature. Third Generation: StealthHide itself from detection.
  11. 11.  Fourth Generation: ArmoredAdd confusing and unnecessary code to make it more difficult to analyze and detect the virus code.Direct attack against Anti-virus software. Fifth Generation: PolymorphicSelf mutating viruses.Their modified version or encrypted version.Difficult to identify
  12. 12. These viruses are not limited to computers orlaptop only. Virus can attack any hand helddevice as well.The more we know about viruses the more wecan protect our devices from it.
  13. 13.  http:// “Computer Viruses as Artificial Life” - Eugene H. Spafford , Department of Computer Sciences Purdue University