Trojans are malware that disguise themselves to gain access to a user's computer without their awareness. They spread by tricking users into downloading email attachments or clicking on fake advertisements. Once installed, they can allow hackers to access personal information, delete files, or use the computer as an anonymizing proxy for illegal activities. Examples include Zeus, which steals banking credentials, and CryptoLocker ransomware, which encrypts files until a ransom is paid. Trojans demonstrate that no system is immune, as shown by the Mac Flashback Trojan.

1. Trojan

2. A malware which misleads users of its true intent.
The term is derived from the Ancient Greek story of
Trojan Horse that led to the fall of the city of Troy
Trojans are generally spread by –
- a user is duped into executing
an email attachment disguised to appear not suspicious,
(e.g., a routine form to be filled in)
- by clicking on some fake advertisement
Their payload act as a backdoor, contacting a controller
which can then have unauthorized access to the affected
computer.
Trojan

3. Unlike computer viruses and worms, trojans generally do not attempt to inject
themselves into other files
Trojan viruses, in this way, may require interaction with a malicious controller
(not necessarily distributing the trojan) to fulfill their purpose. It is possible for
those involved with trojans to scan computers on a network to locate any with
a trojan installed, which the hacker can then control, creating a so
called botnet.
A botnet is a number of Internet-connected devices, each of which is running
one or more bots. Botnets can be used to perform Distributed Denial-of-
Service (DDoS) attacks, steal data, send spam, and allow the attacker to
access the device and its connection. The owner can control the botnet using
command and control (C&C) software
Trojans may allow an attacker to access users' personal information such as
banking information, passwords, or personal identity.
It can also delete a user's files or infect other devices connected to the
network. Ransomware attacks are often carried out using a trojan.

4. Some trojans take advantage of a security flaw in older versions
of Internet Explorer and Google Chrome to use the host computer
as an anonymizer proxy to effectively hide Internet usage,
enabling the controller to use the Internet for illegal purposes
while all potentially incriminating evidence indicates the infected
computer or its IP address.
An anonymizer proxy is a tool that attempts to make activity on
the Internet untraceable. It is a proxy server computer that acts as an
intermediary and privacy shield between a client computer and the rest of the
Internet. It accesses the Internet on the user's behalf, protecting personal
information of the user by hiding the client computer's identifying information

5. According to a survey conducted by BitDefender from January to
June 2009, "trojan-type malware is on the rise, accounting for
83% of the global malware detected in the world."
Trojans have a relationship with worms, as they spread with the
help given by worms and travel across the internet with them.
The host's computer may or may not show the internet history of
the sites viewed using the computer as a proxy. The first
generation of anonymizer trojan horses tended to leave their
tracks in the page view histories of the host computer. Later
generations of the trojan tend to "cover" their tracks more
efficiently.

6. Examples of Trojan Horse Virus Infection
Trojan
Infection
Exploit
Backdoor
Rootkit
Trojan
Banker
Trojan
DDoS
Trojan
Downloa
der
Trojan
Dropper

7. Remote Access Trojan
Data Sending Trojan
Destructive Trojan
Proxy Trojan
FTP Trojan
Security Software Disabler Trojan
DoS Attack Trojan
Types of Trojan

8. Victim Attacker
TCP
Trojan Server Trojan Client
Components of Trojan Horse

9. Zeus
Zeus is a Trojan horse made to infect Windows computers so that
it will perform various criminal tasks.
The most common of these tasks are usually man-in-the-browser
keylogging and form grabbing.
The majority of computers were infected either through drive-by
downloads or phishing scams.
First identified in 2009, it managed to compromise thousands of
FTP accounts and computers from large multinational
corporations and banks such as Amazon, Oracle, Bank of America,
Cisco, etc.
Controllers of the Zeus botnet used it to steal the login credentials
of social network, email and banking accounts.

10. NetBus

11. Back Orifice XP

12. Sub Seven (Sub7)

13. Beast

14. CryptoLocker
CryptoLocker is a form of Trojan horse ransomware targeted at
computers running Windows. It uses several methods to spread
itself, such as email, and once a computer is infected, it will
proceed to encrypt certain files on the hard drive and any mounted
storage connected to it with RSA public key cryptography.
While it is easy enough to remove the malware from the computer,
the files will still remain encrypted. The only way to unlock the files
is to pay a ransom by a deadline. If the deadline is not met, the
ransom will increase significantly or the decryption keys deleted.
The ransom usually amount to $400 in prepaid cash or bitcoin.

16. Flashback
• One of the few Mac malware
• It showed that Macs are not immune.
• The Trojan was first discovered in 2011 by antivirus company
Intego as a fake Flash install.
• In its newer incarnation, a user simply needs to have Java
enabled. It propagates itself by using compromised websites
containing JavaScript code that will download the payload. Once
installed, the Mac becomes part of a botnet of other infected
Macs.