In computing, a Trojan horse, or Trojan, is any malicious computer program which misleads users of its true intent. The term is derived from the Ancient Greek story of the deceptive wooden horse that led to the fall of the city of Troy.
Trojans are generally spread by some form of social engineering, for example where a user is duped into executing an e-mail attachment disguised to be unsuspicious, (e.g., a routine form to be filled in), or by drive-by download. Although their payload can be anything, many modern forms act as a backdoor, contacting a controller which can then have unauthorized access to the affected computer. Trojans may allow an attacker to access users' personal information such as banking information, passwords, or personal identity (IP address). Ransomware attacks are often carried out using a Trojan. Most affected antivirus from Trojan is Webroot and Norton.
The principle of principle of least privilege should normally mean that most users do not have access to install a root kit, completely crash the computer or device, delete all data or format the disk - but many home users, and some corporate laptop users will have this power.
It can perform following task in user's computer or laptop
1. Block all the Anti Viruses
2. Block any program installation processes
3. Steal banking password or card information
4. Breach the security of all the devices
5. It infects all the other computers & devices connected to the same network, by using the infected computer as proxy this trojans send infection to other Computers and Devices.
6. It can send email password to hackers
7. Misuse of user's data like - email, photo, name and other apps like Facebook, skype etc.
8. It can infect multiple devices on the same network by infecting IP addresses.
9. Misuse the computer for crime activity and stealing other people's data
10. Block the inbuilt Firewall security
However, even if the user does not have any special access, they will still have access to read and write all document files which they have legitimate access to - and this is the only access ransomware needs to encrypt them. Similarly, they will may be easily able to read and exploit the user's banking information, and passwords to other systems.
It is also possible that some Trojans will be able to exploit a bug, design flaw or configuration oversight to achieve a privilege escalation to gain elevated access to resources.
If installed or run with elevated privileges a Trojan will generally have unlimited access. What it does with this power depends on the motives of the attacker.
Trojan 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. .
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. 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. Several versions of Sub7 have been widely circulated in the US and Europe and became the most widely distributed examples of this type of Trojan.
In German-speaking countries, spyware used or made by the government is sometimes called govware. Govware is typically a Trojan software used to intercept communications from the target computer. Some countries like Switzerland and Germany have a legal framework governing the use of such software. Examples of govware trojans include the Swiss MiniPanzer and MegaPanzer and the German "state trojan" nicknamed R2D2.
Due to the popularity of botnets among hackers and the availability of advertising services that permit authors to violate their users' privacy, Trojans are becoming more common. According to a survey conducted by BitDefender from January to June 2009, "Trojan-type malware is on the rise, accounting for 83-percent 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. BitDefender has stated that approximately 15% of computers are members of a botnet, usually recruited by a Trojan infection.
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