Do you know a malware type that allows attackers to access systems from remote locations? You should if you plan to take the Security+ exam. This post should help.
Here is a sample practice test question:
Q. A recent antivirus scan on a server detected a Trojan. A technician removed the Trojan, but a security administrator expressed concern that unauthorized personnel might be able to access data on the server. The security administrator decided to check the server further. Of the following choices, what is the administrator MOST likely looking for on this server?
A. Backdoor
B. Logic bomb
C. Rootkit
D. Botnet
Can you answer this question? More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.
Backdoors
A backdoor provides another way of accessing a system, similar to how a backdoor in a house provides another method of entry. Malware such as Trojans often install backdoors on systems to bypass normal authentication methods.
Application developers often code backdoors into applications, but this practice is not recommended. For example, an application developer might create a backdoor within an application intended for maintenance purposes. However, if attackers discover the backdoor, they can use it to access the application.
Effective account management policies help prevent ex-employees from creating backdoors after they are fired. For example, if an employee loses network access immediately after being fired, the employee cannot create a backdoor account. In contrast, if an administrator retains network access, he has the opportunity to create another administrative account that he can use even if his original account is disabled. That’s exactly what a Fannie Mae Unix engineer did after being told he was fired.
Fannie Mae’s account management policy did not revoke his elevated system privileges right away, giving him time to create a backdoor account. After going home, he accessed the system remotely and installed a logic bomb script scheduled to run at 9:00 a.m. on January 31. If another administrator hadn’t discovered the logic bomb, it would have deleted data and backups for about four thousand servers, changed their passwords, and shut them down.
Remember this
A backdoor provides another of way of accessing a system. Many types of malware create backdoors, allowing attackers to access systems from remote locations. Employees have also created backdoors in applications and systems.
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Botnets
A botnet combines the words robot and network. It includes multiple computers that act as software robots and function together in a network (such as the Internet), often for malicious purposes. The computers in a botnet are called zombies and they will do the bidding of whoever controls the botnet.
Bot herders are criminals who manage botnets. They attempt to infect as many computers as possible and control them through one or more servers running command-and-control software. The infected computers periodically check in with the command-and-control servers, receive direction, and then go to work. The user is often unaware of the activity.
Most computers join a botnet through malware infection. For example, a user could download pirated software with a Trojan or click a malicious link, resulting in a drive-by download. The malware then joins the system to a botnet.
As an example, Coreflood malware is a Trojan horse that opens a backdoor on compromised computers. Authorities shut down the Coreflood botnet in April 2011, and its command-and-control servers managed about 2.3 million computers at that time. Experts estimate they had stolen between $10 million and $100 million before authorities shut them down.
Infecting 2.3 million computers and stealing tens of millions of dollars draws a lot of attention. To avoid attention, many botnets manage fewer than 50,000 computers and fly under the radar of most authorities. The result is the same for the victims, though. It doesn’t matter if victims are robbed by a huge botnet or a smaller botnet; they have still been robbed.
Botnet herders sometimes maintain complete control over their botnets. Other times, they rent access out to others to use as desired. Some of the instructions sent by the command-and-control servers include:
- Send spam.
- Launch a distributed denial-of-service attack.
- Download additional malware, adware, or spyware such as keyloggers.
Polymorphic Malware
Some virus developers use polymorphism as a method of armor. Polymorphic malware has the ability to morph or mutate when it replicates itself, or when it executes. The goal is to create a virus or other malware with enough variations that AV software cannot detect it as the same malware. Over time, a single malware file could have thousands of variants.
Virus developers typically encrypt polymorphic viruses as an additional layer of armor to evade detection by AV software. The virus includes a decryption method that executes when the file executes. A common polymorphic technique is to vary the encryption/decryption method slightly. This method retains the original malicious code, but modifies the file enough to make it difficult to detect.
Q. A recent antivirus scan on a server detected a Trojan. A technician removed the Trojan, but a security administrator expressed concern that unauthorized personnel might be able to access data on the server. The security administrator decided to check the server further. Of the following choices, what is the administrator MOST likely looking for on this server?
A. Backdoor
B. Logic bomb
C. Rootkit
D. Botnet
Answer is A. The security administrator is most likely looking for a backdoor because Trojans commonly create backdoors, and a backdoor allows unauthorized personnel to access data on the system.
Logic bombs and rootkits can create backdoor accounts, but Trojans don’t create logic bombs and would rarely install a rootkit.
The computer might be joined to a botnet, but it wouldn’t be a botnet.
