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The damage that a
virus can do
Depending on the virus, the sort of damage or harm that they can do includes the
following:
- Delete files from the computer, or rename files.
- Add itself to the end of a program file, and change the program so that the virus will execute instead of the
program.
- Corrupt program files so that they will not run at all (including the many files that comprise the Windows
environment, so Windows won't run properly).
- Display a message on the computer's screen.
- Render all files on the computer unreadable (e.g. by changing or corrupting the hard drive's File Allocation
Table).
- Stay in the computer's memory so that every time another program is run, the virus will infect that program
as well (i.e. it is memory resident).
- Automatically send an e-mail to all of the people in your e-mail program's address book (this only applies
to some specific e-mail client programs).
- Pick up bits of text from various files on your computer (or from other e-mail messages) and use them to construct
a new e-mail message to automatically send to people in your address book.
- The virus can remain dormant until it receives a message over the Internet to commence it's pre-programmed
activity, which could be a coordinated Denial
of Service (DoS) attack against a particular Web server. This is a real possibility for computers that are
always connected to the Internet via a cable modem, or perhaps by a long-held dial-up telephone call connection.
How do viruses
get into a computer?
A computer can become infected by a virus via the following means:
- A virus can be included as a macro inside a document file or spreadsheet file that is itself attached to an
e-mail message. The sender of the e-mail has probably intentionally attached the file to the e-mail message; but
unknowingly included the virus in the attachment. When the attached file is opened, the macro can automatically
run, and can then cause the virus to infect the computer.
- A virus can be included in other types of files, in particular executable or program files. These files can
also be included as attachments to an e-mail message. When they are executed, they cause the virus to infect the
computer.
- A virus-infected file can be automatically sent to another computer via e-mail, without the sending person
realising that it has happened.
- A virus-infected file (e.g. document, spreadsheet, program, etc.) can also be copied onto a computer over a
network (e.g. a LAN), or from a floppy disk or other removable media (e.g. tape, or other removable disk/diskette).
Early virus infections happened when people passed on simple games programs on a floppy disk.
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