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(c) It may disable the antivirus software on the host, which will enable it to cause more damage.
(d) Bulk email chaining can be created with an intention to guess email passwords.

(e) A worm consumes too much system memory (or network bandwidth), causing web servers,
network servers and individual computers to stop responding.
3. Trojan Horse

A Trojan horse is a kind of virus that looks safe but has hidden effects. It is a hidden code in a program
such as a game or a spreadsheet that can damage the system when running these applications. It
can destroy or alter information on a computer system in the background. Unlike viruses, Trojans
do not replicate themselves but they are destructive. Trojans are executable programs, which
means that when a user runs any application or plays games, they work behind that application
and can damage the system completely.
There are several types of Trojan Horse:

(a) Remote access Trojan horse
(b) Data sending Trojans

(c) Destructive Trojans

(d) Proxy Trojans
(e) FTP Trojans

(f) Denial-of-service attack Trojans
Trojans are generally spread through email attachments and exchange of disks and information
between computers. Worms can also spread Trojans. The damage caused by Trojans is similar to
that caused by viruses. Sometimes the user is unaware about a Trojan because of its masking effect
as it runs as a hidden code.

CTM: Trojan horse is a hidden code that looks safe but it has some hidden effects while running
applications.

4. Spams

Spam is an unwanted bulk mail which is sent by an unauthorized or unidentified person in order
to eat the entire disk space. In non-malicious form, it floods the internet with many copies of the
same message to be sent to a user which he may not otherwise receive. Generally, it is in the form of
pampering the user with various discount schemes, or commercial advertising, often for dubious
products, get rich quick schemes, etc. Mobile phone spam is a form of spamming that uses text
message service of mobile phone.

Spams can be avoided by using email filtering, spam traps, etc.

CTM: Spam refers to electronic junk mail that eats up the entire computer’s space.

Computer Networks
8.23 COOKIES

A cookie is also known as an HTTP cookie, web cookie, internet cookie or browser cookie. When
the user browses any website, a cookie identifies users and prepares web pages for them which
are then sent to the web server for later use. Cookie is basically a piece of data that is stored by the

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