The concept of a Trojan is important to understand rather than seeing it as a type of virus or spyware. This concept being that the malicious code will embed itself inside a program that will seem legitimate to the user.
A Trojan often referred to as a Trojan horse is malware that will appear to perform a desired functionality for the user, but will instead perform unauthorised access to that user’s computer. The code can embed itself in many ways though. Some software owners are unaware of their code being used where others allow the Trojan code to embed into their own for some commercial gain etc.
Remember that different types of viruses, spyware, worms and rootkits can all enter into a system by using a Trojan. The Trojan is the means for the different types of malicious code to enter your computer. Its not usually the Trojan you have to worry about, but whats inside it.
The user downloads and installs what seems to be a perfectly working screensaver. Unknown to the user as this is being installed the Trojan hidden inside the screen-saver code, installs itself privately and will perform, maybe unnoticed etc.
Another sneaky way for use of Trojans are Driveby Downloads; you are surfing and this can even be legit sites etc; that site that you look up will in fact have embedded code sometimes not even the site owner knows of this embedded code. This page will then be re-directed to some other page without you noticing. This re-direction will then have code on its page to download to your machine and you will be infected in most cases.
Types Of Attacks:
Remote Administration: This type of Trojan will sneak into your machine and give the hacker access to your system from a remote location, another country for example. He/she could have full power to do just about anything with your system while your online.
Used As a File Server: When your machine is infected with this malicious code it sets up an FTP server or similar (file transfer protocol). This can then be used to upload files etc or download files etc from your computer.
Email Sending To Hacker: These are usually used to steal information etc from your system and actually send emails from your machine with this information to a computer somewhere else of the hackers choosing.
Key Logger: This is a spying program to record all of your keystrokes that you type into your keyboard. The hacker can then either email from your machine or they may have access to download them remotely.
Distributed Denial Of Service: This is a real scary one, because the hacker can have an army of infected computers on the Internet or local network. They can get them to work as a team to attack one machine, many or attack themselves. This one can be very powerful.
Usually a good Anti-Virus program will deal with these baddies. If not you may need to run the Anti-Virus externally from the computer. E.G you could turn the infected hard-disk into an external for another uninfected computer to scan it.
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