NEC VERSA S5500 Series User Manual page 99

Computer Viruses
When did a virus appear for the first time?
There are theories that experiments with virus-like self-replicating programs already took place in 1949.
Experimental viruses were first programmed and tested in the 1960s. The name 'virus' first popped up in
1984 when a university professor used this term to describe the destructive PC programs. When personal
computers became popular in the 1980s, PC viruses also started appearing. The use of floppy disks and
bulletin boards in the late eighties and the excessive growth of the Internet and PC usage at home and in
businesses in the late nineties increased the number of viruses and infected PCs.
What is a computer virus?
Computer viruses are man-made and share some of the behaviours of biological viruses. A computer virus
passes from computer to computer like a biological virus passes from person to person. Similarities also
exist at a deeper level: a biological virus is not a living thing and has to reproduce itself by infecting cells. A
computer virus must be transmitted on top of some other program or document in order to get executed.
Once running, it is then able to infect other programs or documents.
Is my PC virus-free?
Most viruses have strange effects on your PC. On the other hand, many viruses are carefully programmed to
avoid betraying their presence. The solution to this dilemma is not to assume anything, but to rely upon
antivirus software as a diagnostic tool.
What are the different types of viruses?
Boot sector viruses
with its own infected version. The boot sector program is the first piece of software that is loaded when
you start your PC. It is installed on every hard disk, floppy disk or CD. Without a boot sector, a computer
cannot run any software at all. A boot sector virus will only be effective if you start your computer using
an infected floppy disk or an infected bootable CD. An example of a boot sector virus is 'Parity Boot'.
This virus displays the message 'PARITY CHECK' and freezes the operating system.
Macro viruses - a macro is an instruction that carries out program commands automatically. Many
common applications like Word and Excel make use of these macros. Macro viruses are macros that
self-replicate. If a user accesses a document containing a viral macro, the macro virus will be executed.
Any document on that machine using the same application can then become infected. The infection
process only ends when the virus is noticed and all viral macros are eradicated.
Worms - these are the most popular types of viruses. They infect your PC through e-mail. If you double-
click on the attachment in such a mail, the virus starts sending mail to all the entries in your e-mail
program's Address Book. This creates a lot of traffic on the Internet and slows down connection speed. A
famous example is the Code Red worm, which replicated itself over 250,000 times in approximately nine
hours on July 19, 2001.
Trojan Horse - this type of computer virus disguises itself as a funny program, which you can download
from the Internet. It can also present itself as an e-mail attachment. Once the program is running the
virus will for instance format your hard drive. The famous "I Love You" virus is an example of such a
virus. Trojan horses only hit a small number of people because they are discovered quickly.
Hoax - a hoax is not a typical computer virus, but it can act as one. You may have already received an
email from a friend warning you of a new virus. In most cases you are requested to forward this e-mail to
all entries in your Address Book. Most of these warnings are a hoax and won't do any damage to your
PC. Computers users who are unaware of these hoaxes tend to forward such e-mail to others, thus
creating a lot of traffic on the Internet and slowing down connection speed.
- a boot sector virus infects your computer by replacing the boot sector program
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