A class Presentation

2. Computer Viruses and
Environmental Hazards

4. Name of the Group Members
Md. Selim Reza Bappy

5. Computer Viruses and Infest stations
VIRUS stands for Valuable Information Resources Under Seize. A
virus is a program which produces its own code by attacking itself
to other programs in such a way that the virus code is executed. In
other words, Viruses are programs that share some or all of the
following characteristics with real viruses:
 They have destructive behavior.
They rely on a host to survive and spread. Executing the host program
will also activate the virus program, without the user knowing.
They can protect themselves.
They can protect themselves against attempts to detect and remove them.
Not all viruses have all these characteristics because virus
technology changes to fast.

6. Viruses come in many different forms, but they all potentially have two phases to their
execution:
Infection Phases
When the virus executes, it will infect other programs. Some
viruses Infect other programs each time they are executed; others infect
only upon a certain trigger. This trigger could be anything-a day or time, an
external event on the pc or a counter within the virus.
Many viruses reside the memory of the pc just as terminate-and-stay-
resident(TSR) program that is loaded into memory but is not immediately
executed, such as screen saver. This means that the viruses can wait for
some external event such as inserting a diskette, copying a
file or executing a program to actually infect another
program. These viruses are very dangerous since it is
hard to guess what trigger condition they use for their
infection. Resident viruses frequently corrupt the
system software on the pc to hide their existence.