viruses

Types of viruses :-
The different types of viruses
areas follows-
1) Boot Sector Virus :- Boot sector
viruses infect
either the master boot record of
the hard disk or
the floppy drive. The bootrecord
program
responsible for the booting of
operating system is
replaced by the virus. The
viruseither copies the
master boot program to another
part of the hard
disk or overwrites it. They infect a
comput...
er when it boots up or when it
accesses the
infected floppy disk in the floppy
drive. i.e. Once
a system is infected with a boot-
sector virus,any
non-write-prote cted disk
accessed by this system
will become infected.
Examples of boot- sector viruses
are Michelangelo
and Stoned.
2) File or Program Viruses :- Some
files/programs,
when executed, load the virus in
the memory and
perform predefined functions to
infect the system.
They infect program files with
extensions
like .EXE, .COM, .BIN,.DRV and .SYS .
Some common file viruses are
Sunday, Cascade.
3) Multipartite Viruses :- A
multipartite virus is a
computer virus that infects
multiple different
target platforms, and remains
recursively infective
in each target. It attempts to
attack both the boot
sector and the executable, or
programs, filesat the
same time. When the virus
attaches to the boot
sector, it will in turn affect the
system’s files, and
when the virus attachesto the
files, it will in turn
infect the boot sector.
This type of virus can re-infect a
system over and
over again if all parts of the virus
are not
eradicated.
Ghostball was the first
multipartite virus,
discovered by Fridrik Skulason in
October 1989.
Other examples are Invader, Flip,
etc.
4) Stealth Viruses :- These viruses
are stealthy in
nature means it uses various
methods for hiding
themselves to avoid detection.
They sometimes
remove themselves from the
memory temporarily
to avoid detection by antivirus.
They are
somewhat difficult to detect.
When an antivirus
program tries to detect the virus,
the stealth virus
feeds the antivirus programa
clean image of the
file or boot sector.
5) Polymorphic Viruses :-
Polymorphic viruses have
the ability to mutate implying that
they change
the viral code knownas the
signature each time
they spread or infect. Thus an
antivirus program
which is scanning for specific
virus codes unable
to detect it's presense.
6) Macro Viruses :- A macro virus
is a computer
virus that"infects" a Microsoft
Word or similar
application and causes a sequence
of actions to
be performed automatically when
theapplication is
started or something else triggers
it. Macro
viruses tend to be surprising but
relatively
harmless.A macro virus is often
spread as an e-
mail virus.Well-know n examples
are Concept Virus
and Melissa Worm