Friday, November 25, 2005

Backdoor Trojans

One newer type of Trojan horse is a backdoor Trojan, which installs an executable file on systems. By altering the Registry (Windows central database for system settings and user preferences), the backdoor Trojan also launches when you start your computer.
A backdoor can be any “loophole” in software code that lets an unauthorized user access a system by opening a port or connecting to the Internet. Some programs contain backdoors that developers accidentally created while writing the software code. This is why users should check companies’ web sites regularly for any new software patches they can download and install. As software manufacturers find such security threats, they release patches that correct errors. Of course, not all backdoors appear accidentally within software; hackers purposely create backdoors for malicious purposes.
Hackers can use programs called sniffers to locate open ports and gain access to systems using backdoors. When hackers activate backdoor Trojans on infected systems, its code opens a port or connects to the Internet. Normally, these actions take place in the background, so a user doesn’t realize immediately that his computer is infected. In fact, often after the Trojan horse runs, nothing happens right away. Instead, the system waits for a hacker (either the originator of the Trojan or a different hacker using a sniffer) to take control of the system and start an attack.
The most obvious reason why a hacker might use a backdoor Trojan to access a system is to gain access to sensitive files and data, such as financial records, passwords, and credit card numbers. Another common use of backdoor Trojans is to turn computers into virtual zombies a hacker could use to launch a DoS (denial of service) or DDoS (distributed denial of service) attack. To define what zombies and DoS attacks are and explain how a hacker could use a backdoor Trojan as the means to these ends, let’s break down the process step by step.
First, a backdoor Trojan opens a system to outside access so a hacker can control the computer remotely from his/her computer. When a hacker manipulates a system in this way, it becomes a zombie. The hacker can use a zombie to launch a DoS attack by sending abnormally large quantities of data or PING (Packet Internet Groper; echo request message to a target to check the status of a network connection) requests to a specified computer or server. If a hacker simultaneously uses multiple zombies for this purpose, the process becomes a DDoS attack, which makes it harder to trace the true source of the attack. Such a flood of Internet traffic may slow down a server (causing a degradation of service) or cause the server to crash.
Even if the hacker only succeeds at causing a degradation of service rather than causing a server to crash, the results are still costly. For instance, if traffic on Amazon.com slows to a certain level, the company will lose money as customers become frustrated with the site’s online service and decide to take their business elsewhere.
A hacker might target other types of servers or home computers, as well. Sometimes a hacker’s goal isn’t to bring down a company, but simply prove that he/she can use zombies to control the Internet service others receive. He/she will likely avoid detection because it is difficult to trace this type of activity when a hacker distributes it among many zombies.
Although backdoor Trojans are a relatively new type of Trojan horse, that doesn’t mean that they are rare. Let’s look at just a few backdoor Trojan horses to further analyze this type of malware.

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