Viruses are computer programs that can replicate themselves and infect computers without permission. They enter systems through email attachments or downloads. Viruses have four components: replication, payload, trigger, and infection mechanism. The payload can damage systems, while the trigger activates the payload under certain conditions. There are different types of viruses like boot sector viruses that infect hard drives, macro viruses that use application code, and file infector viruses that attach to executable files. System updates, firewalls, antivirus software, and caution with email attachments can help combat viruses.

2. Viruses allow the intruders to access the computer
system and resources. Viruses enter into the computer
system without the user’s permission or knowledge.
Viruses are computer programme that can replicate
itself and infect the computer.
The purpose of virus may be destructive. It includes
slow down the computer system and destroying the hard
disk.

3. Structure of Virus
Virus
Replication Payload Trigger

4. It describes the way in which virus spread .
It is the first stage through which the virus propagates.
Virus mainly spread through email attachments or
viruses attach them to the download such as movie etc.

5. It contain intended action or actual purpose.
The payload can create accidental or intentional
damage.

6. It describe the mechanism by which payload is activated.
The payload is triggered or activated on same conditions
which include certain date or time, opening an email
attachment etc.
Trigger component us related to infection mechanism
means that virus needs to be executed.

7. Virus
Dormant
Phase
Propagation
Phase
Triggering
Phase
Executing
Phase

8.  Dormant Phase
In this phase virus remains idle. It includes that virus
doing nothing until the user executes the file
 Propagation Phase
In this phase virus gets activated and starts replicating
itself. In this virus places a copy of itself into another
programme or into certain areas in the disk.

9. In this virus executed its payload. In this virus performs
the actual function which may be harmful.
In this virus gets activated to perform the function for
which it was intended. The event for which virus was
waiting gets initialized

10. Types of
virus
Boot Sector
Virus
Partite or
Multi
Partite
Virus
Stealth
Virus
Macro
Virus
File
Infector
Virus

11. File Infector virus
These type of virus attach themselves to files or these
virus basically attack the executable file. It is further
divided into different categories:-
Direct Action File Infector
Resident Infectors

12. Boot Sector Virus
This virus is always executed and locate in the memory
when the system start. It infects the hard drive of the
computer. These virus replace boot sector programme
with corrupted version.
Macro Virus
It is a virus that is written in macro language. Macro
language is mixed with software application like MS-
Word and MS-Excel.

13. These virus infect both boot sector and programme files. It
is difficult to repair. In this boot area and files must both
be cleaned of virus or re-infection will occur.
In this movement of virus is quite and careful in order not
to be seen or heard

14. Tips to Combat Virus
The operating system, applications and software of
computer system should be update.
Firewalls should be used.
Anti-virus must be installed in the computer system.
E –mail programme should not be set to auto run
attachment.
Each file and software should be scanned before
downloading.