A computer virus is a program that disrupts normal computer operations by infecting and destroying data and entering computers without user permission or knowledge. Viruses self-replicate by infecting more files, slowing computers down and destroying data. They enter via infected floppy disks or the internet/email. Viruses remain inactive until triggered to harm data and programs. Antivirus software identifies, prevents, and removes viruses by scanning files against known virus definitions and suspicious program behaviors.

2. A computer virus is a program or a set of programs
that disrupts the normal operation of a computer .
Virus infects or destroys data . It enters in the
computer without the permission or knowledge of
the user . stands for Vital Information
Resources Under Seize. The essential resources like
memory, processing speed, data & programs etc. cannot
have normal operations and can be harmed when virus is
spread. Viruses are self-replicating & are continuously
expanding their reach by infecting more computer files,
resulting in loss of speed & destruction of data. It enters
through an infected floppy or Internet / E-mail.

3. Virus remains undetected & quietly inactive & waits for a particular signal
or an event to trigger them. Some virus programs monitor the clock in the
host computer & trigger on a certain day, like Friday the 13th. A biological
virus causes physical harm to our body and attack certain cells, whereas
computer virus causes harm to the data and programs stored in computer
by over writing them with garbage or erasing them.
Trojan Horses, Worms & Spyware are some other terms which are
associated with virus programs but are actually different from virus
programs.
Trojan Horse : They are non replicating simple but destructive programs
which spreads from one system to another when it is copied.
Worm : Is a special virus that can replicate itself and use memory but cant
add itself to other programs.
Malware : Is a trouble causing program which interrupt the normal working
of a computer by stealing important information and damages it without the
knowledge of the user.

4. Spyware: It is a type of malware that is installed on computers and collects
information about users without their knowledge. They secretly monitor the
user’s computing and also collect various types of personal information about
internet surfing habits, visited web pages and transmits the same in the
background to someone else.
Types of viruses :
Viruses can be classified into two major categories.
1. Boot Viruses:
They infect the boot record or master boot records by replacing the same
which is responsible for loading the operating system in memory by copying it
elsewhere. Examples are – Disk killer, Stoned virus.
2. Program File Viruses:
They infect executable files, programs such as those with extension like .com,
.exe, .ovl, .drv, .sys etc. These programs get loaded during execution and
becomes active by replicating, also infecting files on the disk. Sunday, Cascade
etc. are the examples of Program file virus.

5. VIRUS SYMPTOMS:
The symptoms of virus infection in computer can be detected in many ways such as
Decreasing computer speed, causing strange movements or patterns on screen,
displaying unusual messages, frequent hanging of the system, Reformatting the hard
disk, deleting or damaging files etc.
PREVENTING A VIRUS INFECTION :
To prevent virus infection every pc should be equipped with some anti-virus
program, perform scan for virus infection before running or copying files from
external devices, not installing pirated software, perform periodical scanning hard
disk, using internet and e-mail attachments very carefully.
ANTIVIRUS SOFTWARE :
Antivirus software are computer programs which are designed to indentify, prevent
and remove viruses from our computer.
Antivirus programs scan the computer files to look for known viruses matching
definitions from virus dictionary and also identify suspicious behavior from any
computer program which indicates infection.