COMPUTER VIRUSES,WORMS AND TROJAN HORSES

• Computer viruses - can damage computer program that affects or infects a computer negatively by altering the way the computer works without the user's knowledge or permission.it can spread throughout and may damage files and system software including the operating system.
• worms -program that copies itself repeatedly-possibly shutting down the computer or network.
• Trojan Horses - programs that hides within or look likes a legitimate program(program yang sah).
• Computer viruses, worms and trojan horse are classified as malware.
• Symptoms of computer infected :

-screen displays unusual message or image.
-music or unusual sound plays randomly.
-available memory is less.
-programs or files disappear
-files become corrupted
-programs or files do not work properly
-system properties change.

• They can spread when 1)open an infected file 2)run infected program 3)boots the computer with infected removable media in a drive or port 4)connects unprotected computer to a network.

reference : discovering computer (shelly cashman vermaat)