Virus..Trojan..Worm

What is a computer virus?

A computer virus is a small software program that spreads from one computer to another computer and that interferes with computer operation. A computer virus may corrupt or delete data on a computer, use an e-mail program to spread the virus to other computers, or even delete everything on the hard disk.  

Symptoms of a computer virus

If you suspect or confirm that your computer is infected with a computer virus, obtain the current antivirus software. The following are some primary indicators that a computer may be infected:
  • The computer runs slower than usual.
  • The computer stops responding, or it locks up frequently.
  • The computer crashes, and then it restarts every few minutes.
  • The computer restarts on its own. Additionally, the computer does not run as usual.
  • Applications on the computer do not work correctly.
  • Disks or disk drives are inaccessible.
  • You cannot print items correctly.
  • You see unusual error messages.
  • You see distorted menus and dialog boxes.
  • There is a double extension on an attachment that you recently opened, such as a .jpg, .vbs, .gif, or .exe. extension.
  • An antivirus program is disabled for no reason. Additionally, the antivirus program cannot be restarted.
  • An antivirus program cannot be installed on the computer, or the antivirus program will not run.
  • New icons appear on the desktop that you did not put there, or the icons are not associated with any recently installed programs.
  • Strange sounds or music plays from the speakers unexpectedly.
  • A program disappears from the computer even though you did not intentionally remove the program.

Symptoms of worms and trojan horse viruses in e-mail messages

When a computer virus infects e-mail messages or infects other files on a computer, you may notice the following symptoms:
  • The infected file may make copies of itself. This behavior may use up all the free space on the hard disk.
  • A copy of the infected file may be sent to all the addresses in an e-mail address list.
  • The computer virus may reformat the hard disk. This behavior will delete files and programs.
  • The computer virus may install hidden programs, such as pirated software. This pirated software may then be distributed and sold from the computer.
  • The computer virus may reduce security. This could enable intruders to remotely access the computer or the network.
  • You receive an e-mail message that has a strange attachment. When you open the attachment, dialog boxes appear, or a sudden degradation in system performance occurs.
  • Someone tells you that they have recently received e-mail messages from you that contained attached files that you did not send. The files that are attached to the e-mail messages have extensions such as .exe, .bat, .scr, and .vbs extensions.