Botnet attacks make a machine or network resource unavailable to its intended users. Botnets can be used to perform various tasks like:
1. Amplification: Dumps massive traffic from zombie machines to the target. This is mainly done using UDP reflection/amplification techniques.
2. Nefarious Activities: Spamming, Phishing. These are the activities that are being done using botnets for illegal purposes.
3. DoS Attacks: Zombies are made to send many requests to the target machine quickly to exhaust its resources and make it unavailable for legitimate users.
4. Distributed Brute-force attacks: In these types of attacks, requests with different user agents and crafted requests are sent to the target machine, which consumes many resources during the log-checking. Zombies make repeated login attempts against a list of common passwords or usernames to exploit a security vulnerability in the server’s password normalization function.
How does a Zombie work?
Attackers can take control of a machine in many ways: attackers have to own a zombie computer to perform any attack. A compromised machine becomes part of the botnet after getting controlled by an attacker to conduct illegal activities like spamming or launching DoS attacks against other devices. The process is called Botting. Usually, it is done with the help of bots or Trojan horses. In some cases, attackers also use backdoors to manage zombies remotely.
Any computer device running on any OS, like PCs, Notebooks, etc., could be used as a zombie machine to perform an attack. Attackers tend to choose either Windows-based operating systems or Linux-based OS as zombies, but it is not mandatory.
Attackers use computers with a fast network interface to send and receive data packets from the target machine. For example, the Gbit/s speed of the network card could be used by an attacker to increase the amount of traffic that can be sent to a victim.
Tools like low-orbit ion cannon (LOIC) or Trin00 can be used to perform a DDoS attack.
Types of botnets
There are many types of botnets available in the market. Listed below are some of them:
Sending spam: In this type of botnet, many zombie machines are used to send spam emails that carry a malicious attachment or link. Usually, these emails are sent with spoofed sender addresses to avoid getting tracked by anti-spam software. This type of botnet is considered very dangerous for an organization as it can target employees and compromise the company’s sensitive data.
Cyber-espionage: Mainly used by the nations against other nations, Cyber Espionage includes the following activities:
They are hacking into government or military computers to get secret information like defense plans, lists of spies, etc.
Compromising someone’s email and getting access to all the data stored in it, like credit card information, personal and official documents, and so on, can be used for monetary gain or spying purposes.
DoS attack: This type of botnet is mainly used by attackers to exhaust a target machine’s computational resources to make it unavailable for legitimate users.
DDoS attack: Attackers mainly use this to make a network resource unavailable through amplification techniques. For example, the attacker will send requests to open a port with a source IP address spoofed as the victim’s address, amplified by vulnerable UDP servers on the way back to the target machine, making it unavailable. Thus, it will magnify the traffic the attacker can send to the victim’s engine, exhausting its resources and making it inaccessible to legitimate users.
Spreading Malware: Hackers use botnets to apply malicious codes like viruses, Trojan horses, etc. Many zombie machines are made to visit pre-defined malicious websites containing malicious codes. When a user visits these sites, the infection starts automatically and successfully installs malware on his device in the background without the user’s knowledge, causing various problems.
How to defend against a botnet attack?
It is necessary to follow some steps to make an organization immune to botnet attacks.
Scan network devices regularly: It is essential to scan routers, switches, firewalls, and other network devices periodically to identify any unknown device connected with the internal network that might act as a botnet. Also, the user should look at device configurations and check if they allow anonymous internet access.
Configure routers and firewalls: Network devices like routers and firewalls should be appropriately configured to make them immune to DDoS attacks. It is essential to perform port filtering on routers and set up packet filtering rules on firewalls for blocking unwanted ports and IP addresses. Also, management should keep in mind that any open port on network devices might spread malware, which eventually results in the spread of botnets and infection of other machines in the internal network.
Establish security policies: It is necessary to establish security policies like access and patch management policies. With the help of these policies, users can define acceptable usage policies for machines and employees to avoid being affected by malware.
Train users: It is necessary to train users about the latest threats in the market because it is possible that unknowingly, a user might download and install some software that might not be safe and eventually affect the whole internal network. Train them about Virus Protection, downloading and installing applications, using email attachments, and so on.
Install Intrusion Detection System (IDS): It is necessary to install IDS at various places in the network to block any malicious communication between bots and the C&C center, which usually happens after installing malware. Also, it can block communication if a new command is different.
Takeaways and tips for preventing a Botnet attack on your computer:
Enable firewall: Always keep a personal firewall enabled on your machine to protect the device from unauthorized access over the internet. It creates a security perimeter or network to monitor and control traffic. If there is any suspicious activity, the firewall will block that connection to make the system safe.
Use strong passwords: Users should always use strong passwords to protect the device from unauthorized access because it is the first line of defense to protect machines from botnet attacks. A strong password should have alphanumeric characters, and special characters should be long enough and must not contain any dictionary words or names.
Avoid clicking on links in emails: Users should always avoid clicking on links in emails received from unknown users because it might be a trick for hackers to spread malware over the internet. Always check the link address before clicking any link inside an email because hackers usually use URL shorteners to mask actual IP addresses, which results in the redirection of the website and eventually infects your machine with a botnet.
Regularly update Antivirus software: Always install an antivirus program on your machine to protect it from viruses and malware. Updating the antivirus software regularly is necessary because hackers quickly enter network devices through an older software version. So, always keep Antivirus up to date irrespective of your operating system.
Limit open ports: The user should always limit the available ports in the network devices like routers and firewalls to secure them from unauthorized access. If any port is not in use, the user should close that particular port because opening more than the required ports makes the device vulnerable to attack.
Use strong encryption: Always use a suitable encryption mechanism to protect your essential data from others because encryption will secure your data from being accessed or modified by unauthorized users.
Always keep a backup: If you have any critical data in the system, then always keep a backup for that data because if, for some reason, malware gets installed on the design and corrupts all data, then users can recover it through a backup file.
Conclusion
A botnet attack can be prevented to a greater extent in an organization when the administrator strictly implements a security policy. There is no 100% protection from these attacks, but a good botnet attack protection software can help you avoid the risk as much as possible. Also, users must follow some precautionary steps that can help them avoid being affected by malware.