Computer Virus
1. What is a computer virus?
A computer virus is a program designed to spread itself by first
infecting executable files or the system areas of hard and floppy
disks and then making copies of itself. Viruses usually operate
without the knowledge or desire of the computer user.
2. What kind of files can spread viruses?
Viruses have the potential to infect any type of executable code,
not just the files that are commonly called 'program files'. For
example, some viruses infect executable code in the boot sector
of floppy disks or in system areas of hard drives. Another type
of virus, known as a "macro" virus, can infect word processing
and spreadsheet documents that use macros.Since virus code must
be executed to have any effect, files that the computer treats
as pure data are safe. This includes graphics and sound files such
as .gif, .jpg, .mp3, .wav, etc., as well as plain text in .txt
files. For example, just viewing picture files won't infect your
computer with a virus. The virus code has to be in a form, such
as an .exe program file or a Word .doc file, that the computer
will actually try to execute.
3. How do viruses spread?
When you execute program code that's infected by a virus, the virus
code will also run and try to infect other programs, either on
the same computer or on other computers connected to it over a
network . And the newly infected programs will try to infect yet
more programs. When you share a copy of an infected file with other
computer users, running the file may also infect their computers;
and files from those computers may spread the infection to yet
more computers. If your computer is infected with a boot sector
virus, the virus tries to write copies of itself to the system
areas of floppy disks and hard disks. Then the infected floppy
disks may infect other computers that boot from them, and the virus
copy on the hard disk will try to infect still more floppies.Some
viruses, known as 'multipartite' viruses, can spread both by infecting
files and by infecting the boot areas of floppy disks.
4. What do viruses do to computers?
Viruses are software programs, and they can do the same things as
any other programs running on a computer. The actual effect of
any particular virus depends on how it was programmed by the person
who wrote the virus. Some viruses are deliberately designed to
damage files or otherwise interfere with your computer's operation,
while others don't do anything but try to spread themselves around.
But even the ones that just spread themselves are harmful, since
they damage files and may cause other problems in the process of
spreading.Note that viruses can't do any damage to hardware: they
won't melt down your CPU, burn out your hard drive, cause your
monitor to explode, etc. Warnings about viruses that will physically
destroy your computer are usually hoaxes, not legitimate virus
warnings.
5. What is a Trojan horse program?
A type of program that is often confused with viruses is a 'Trojan
horse' program. This is not a virus, but simply a program (often
harmful) that pretends to be something else.For example, you might
download what you think is a new game; but when you run it, it
deletes files on your hard drive. Or the third time you start the
game, the program E-mails your saved passwords to another person.
Note: simply downloading a file to your computer won't activate
a virus or Trojan horse; you have to execute the code in the file
to trigger it. This could mean running a program file, or opening
a Word/Excel document in a program (such as Word or Excel) that
can execute any macros in the document.
6. What's the story on viruses and E-mail?
You can't get a virus just by reading a plain-text E-mail message
or Usenet post. What you have to watch out for are encoded messages
containing embedded executable code (i.e., JavaScript in an HTML
message) or messages that include an executable file attachment
(i.e., an encoded program file or a Word document containing macros).
In order to activate a virus or Trojan horse program, your computer
has to execute some type of code. This could be a program attached
to an E-mail, a Word document you downloaded from the Internet,
or something received on a floppy disk. There's no special hazard
in files attached to Usenet posts or E-mail messages: they're no
more dangerous than any other file.
7. What can I do to reduce the chance of getting viruses from E-mail?
Treat any file attachments that might contain executable code as
carefully as you would any other new files: save the attachment
to disk and then check it with an up-to-date virus scanner before
opening the file. If your E-mail or news software has the ability
to automatically execute JavaScript, Word macros, or other executable
code contained in or attached to a message, we strongly recommend
that you disable this feature. If an executable file shows up unexpectedly
attached to an E-mail, you should delete it unless you can positively
verify what it is, who it came from, and why it was sent to you.
The recent outbreak of the Melissa virus was a vivid demonstration
of the need to be extremely careful when you receive E-mail with
attached files or documents. Just because an E-mail appears to
come from someone you trust, this does NOT mean the file is safe
or that the supposed sender had anything to do with it.
Some general tips on avoiding virus infections:
1. Install anti-virus software from a well-known, reputable company,
UPDATE it regularly, and USE it regularly. New viruses come out every
single day; an a-v program that hasn't been updated for several months
will not provide much protection against current viruses.
2. In addition to scanning for viruses on
a regular basis, install an "on access" scanner (included
in most good a-v software packages) and configure it to start automatically
each time you boot your system. This will protect your system by
checking for viruses each time your computer accesses an executable
file.
3. Virus scan any new programs or other files that may contain executable
code before you run or open them, no matter where they come from.
There have been cases of commercially distributed floppy disks and
CD-ROMs spreading virus infections.
4. Anti-virus programs aren't very good at detecting Trojan horse
programs, so be extremely careful about opening binary files and
Word/Excel documents from unknown or 'dubious' sources. This includes
posts in binary newsgroups, downloads from web/ftp sites that aren't
well-known or don't have a good reputation, and executable files
unexpectedly received as attachments to E-mail or during an on-line
chat session.
5. If your E-mail or news software has the ability to automatically
execute JavaScript, Word macros, or other executable code contained
in or attached to a message, I strongly recommend that you disable
this feature.
6. Be _extremely_ careful about accepting programs or other files
during on-line chat sessions: this seems to be one of the more common
means that people wind up with virus or Trojan horse problems. And
if any other family members (especially younger ones) use the computer,
make sure they know not to accept any files while using chat.
7. Do regular backups. Some viruses and Trojan horse programs will
erase or corrupt files on your hard drive, and a recent backup may
be the only way to recover your data.
Ideally, you should back up your entire system on a regular basis.
If this isn't practical, at least backup files that you can't afford
to lose or that would be difficult to replace: documents, bookmark
files, address books, important E-mail, etc.
Dealing with virus infections:
First, keep in mind "Nick's First Law of Computer Virus Complaints " : "Just
because your computer is acting strangely or one of your programs
doesn't work right, this does NOT mean that your computer has a virus."
1. If you haven't used a good, up-to-date anti-virus program on
your computer, do that first. Many problems blamed on viruses are
actually caused by software configuration errors or other problems
that have nothing
to do with a virus.
2. If you do get infected by a virus, follow the
directions in your anti-virus program for cleaning it. If you have
backup copies of the infected files, use those to restore the files.
Check the files you restore to make sure your backups weren't infected.
3. For assistance, check the web site and support
services for your anti-virus software.
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