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Cyren Security Blog

The Cyren Security Blog is where Cyren engineers and thought leaders provide insights, research and analysis on a range of current cybersecurity topics.

What is a Botnet Attack? 6 Ways to Identify and Prevent It

Botnets have become a trend in 2022 and will likely continue to be a threat in 2023. According to Spamhaus’s Q4 2021 Botnet Threat Update, they reported there was a 23% increase in botnet C&C attacks from Q3 to Q4 in 2021. Additionally, there were 300,000 instances of Emotet observed in 2019, at a surge rate of about 91% compared to the previous year.

The ratio expressed in the saying “an ounce of prevention is worth a pound of cure” is off by several magnitudes when applied to Internet security. While avoiding getting infected in the first place is obviously ideal, evasive tactics invariably fool many security systems. Let’s take a look at what a botnet is and how to detect them.

What is a Botnet?

Botnets are a collection of compromised workstations that are utilized to accomplish a malicious agenda. They are controlled by remote servers which perform malicious acts. Remote commands and a control server can manage botnet computers. The operator of the command and control infrastructure, also known as the bot herder or botmaster, utilizes said compromised computers, or bots, to attack other computers. This is typically done by crashing a target’s network, injecting malware, harvesting credentials or executing CPU-intensive tasks.

How Does a Botnet Attack Work?

Since botnet owners have the ability to access and send commands to several thousand machines simultaneously, they can cause much harm to networks. Initially, botmasters can access these devices by using specific trojan viruses – assaulting the security mechanisms of the computer and then developing software for command and control. This enables them to produce large-scale operations. These actions can also be automated in order to promote as many attacks as possible simultaneously. Various attacks may include:

  • Denial-of-service (DDoS) attacks
  • Spam and virus attacks
  • Stealing any private data from clients

Traditionally, botnets use HTTP and IRC protocols in order to communicate with infected botnet clients. Botnet communication has unfortunately evolved to evade security services. They can find other paths in order to control infected botnet clients on non-traditional network ports, as well as social networks, and PTP networks.

What Are Botnets Used For?

Hackers use botnets to attack a large number of computers at once. These machines are infected with malware and can be controlled by a single attacker. Once the malware infects a computer, bots automatically send spam messages, steal data, and perform other malicious attacks without human intervention.

The 8 Biggest Botnets

1. 3ve

  • Type: click fraud botnet
  • Infected Computers: ~ 2 million


2. Dridex

  • Type: banking trojan
  • Infected Computers: unknown


3. Emotet

  • Type: banking trojan

  • Infected Computers: unknown


4. Mariposa

  • Type: trojan/worm

  • Infected Computers: ~ 11 million (two outbreaks)


5. Mirai

  • Type: DDoS botnet
  • Infected Computers: ~ 560,000


6. Storm

  • Type: email worm

  • Infected Computers: ~ 2 million


7. ZeroAccess

  • Type: trojan downloader

  • Infected Computers: ~ 9 million


8. ZeuS

  • Type: banking trojan

  • Infected Computers: ~ 13 million


Why are Botnets Hard to Detect?

There isn’t a general template for what botnets look like. Every botnet is unique and different when it comes to how it’s set up, how it continues to grow, and why it even exists. This makes it extremely difficult to detect. When it comes to how botnets infiltrate, every security vulnerability is a potential point of entry. Think about how often major companies patch operating systems, then consider how many people don’t install those patches or take a long time to do so. Hackers don’t have to look far to find a device that their botnet can infect.

How to Detect a Botnet On Your Network

Botnet detection can fall into two different categories: Static analysis and behavioral analysis. Static analyses are simple, quick, and resource-friendly. Behavioral analyses go more in-depth but are much more resource-intensive.

1. Static Analysis

Botnet detection can fall into two different categories: Static analysis and behavioral analysis. Static analyses are simple, quick, and resource-friendly. Behavioral analyses go more in-depth but are much more resource-intensive. Static techniques are where you look for a highly specific match to something. This could include a malware signature, specific executable, or a C&C connection address.

Unfortunately, this doesn’t always work. Botnet managers are becoming increasingly sophisticated, using counters like file polymorphism in order to alter the executables in unpredictable ways. Typically, botnet detection by static analysis simply is not enough.

2. Behavioral Analysis

Behavioral analysis is almost always essential to botnet detection. The timing of attacks is typically a dead giveaway. C&C servers usually issue blanket orders for bots, so they take specific actions.

The average interval of time between connecting endpoints to a different outbound server will be low for bots because there is not a human driving the network activity. There will also be failed connection attempts. Those connection attempts are more likely to involve a numerical IP address than a server name. In addition, port-scanning local networks for new infiltration opportunities is the classic behavior for a bot.

3. Built-in IRC Server Scanners

IRC server scanners can identify botnets by looking for non-human behavioral traits within traffic. That said, these servers are a third approach to botnet detection. This identifies secondary characteristics of bot infections, such as attack behavior. Finding command and control traffic is the key to this approach.

4. Traffic Flow Data

Using traffic flow data does not require full security proofs. Effective botnet detection tools can help to measure these traffic patterns and flows to detect unusual behavior that is coming from malicious centers to trigger an attack. 


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4 Common Types of Botnet Attacks

1. Brute Force Attack

A brute force attack is a hacking method that utilizes trial and error to guess passwords and login credentials. It’s a simple yet effective tactic for gaining access to an individual or organization’s account, system, and network. A typical brute force attack can make hundreds of guesses every second. 

2. DDoS Attack 

Distributed Denial of Service attacks can be easily launched using botnets. This type of attack works by overloading a server with web traffic in order to crash it. During this downtime, additional botnet-based attacks can be launched. 

3. Phishing and Spam 

One of the most common delivery methods for phishing campaigns is email spam. These campaigns are crafted to resemble legitimate brands or organizations in order to steal sensitive information or login credentials. Phishing can also compromise more devices in your network to grow the botnet. 

4. Device Bricking 

Cybercriminals can launch bots for a device-bricking attack that can make the device useless. Bricking generally means that a device isn’t recoverable and can’t be fixed, making it useful as a brick.

How to Identify Botnet Traffic

There are different signs, as well as initial symptoms which can all help IT teams recognize a botnet might have infiltrated their network. These typically manifest quickly after botnet infiltration, when the compromised machine begins executing its instructions.

Symptoms of botnet infiltration may include:

  • Linking your network to established C&C servers where they receive instructions
  • Generating Internet Relay Chat (IRC) traffic through a range of different ports
  • Generating identical DNS requests
  • Generating Simple Mail Transfer Protocol (SMTP) traffic and e-mails
  • Reducing workstation performance/Internet access to the point it’s obvious to end-users

To find the bot within, follow the chatter—to detect a bot you should search for the two-way communications that the bot conducts with its command and control (C&C) server. There are several warning signs and methods that an organization can use to uncover the presence of bots.

Check Email Traffic

If your organization’s emails are being rejected by recipient organizations or ISPs, this may indicate that at some point emails from your company were blacklisted, probably as a result of spam activity originating on your network.

Check Botnet Status Sites

When you hear about a large botnet attack, it’s important to check sites to see if you may be a part of the problem. You can then have the ability to mitigate an attack. 

Watch Out For Windows Processes

If you open Task Manager in Windows 10, you have the ability to see which processes are using your network. Take a look at these and determine if anything looks suspicious. If you don’t recognize one of the processes running, do a little research on the Internet to see if the process or behavior is related to a botnet.

Utilize Corporate Firewalls

Corporate firewalls are typically the first line of defense when it comes to your network’s security. It creates a virtual fence in between secure internal networks and any untrusted sources like specific websites or the Internet as a whole. Corporate firewalls also have rule sets for detecting suspicious port use or unknown transactions.

Install an Intrusion Prevention System

Intrusion prevention systems are a form of network security working to detect and prevent identified threats. Intrusion prevention systems continue to monitor networks, looking for any possible malicious incidents and then capturing relevant information about them. This type of system comes with built-in open-source or vendor-defined rules for detecting bot traffic.

Use Web Security/URL Filtering Systems

These types of systems block outbound bot communications to C&C’s and help admins identify where the bots are in order to remove them. Cyber threat intelligence feeds and web categorization/classification engines can help.

Consider Creating a “Darknet” on your Network

By creating a subnet on your LAN that shouldn’t normally have traffic routed to it, with logging machines in it, you can detect which computers aren’t obeying your normal network setup; for example, these computers may be scanning for nodes on the network they intend to infect.

Use Security Solutions from Vendors Who Specialize in Bot Detection

There are vendors who specialize in bot detection and rely on behavioral analysis using the combined approach of log analytics and traffic analysis.

Once unwanted traffic has been detected, the next step is tracking down the source. Cybersecurity solutions offer the best chance to discover who has compromised your network. Preference should be given to solutions that can provide user identification to simplify the process, especially where users are behind network address translation (NAT) devices. Cyren technology is embedded into many cloud services and security products that block outbound bot communications to C&C’s and helps admins identify where the bots are in order to remove them.

6 Botnet Prevention Tips

1. Avoid Opening or Downloading Email Attachments From Suspicious Sources

The anatomy of a phishing email attack could contain invoice attachments that claim you have an outstanding balance due, and in order to resolve the issue, it may contain a link that leads to a fake webpage that is made to steal your banking information. 

2. Avoid Downloads From Peer-to-Peer (P2P) and File-Sharing Networks

Peer-to-peer file sharing is a growing security risk for organizations and individuals. In today’s digital age; music, pictures, and videos are constantly being distributed around the world. This ease of accessibility can make it easier to disguise and spread viruses, worms, and spyware at an alarming rate. 

3. Avoid Clicking on Suspicious Links That Play on Your Emotions

Social engineering attacks use psychological triggers in order to manipulate its victim into divulging confidential information. Phishing campaigns will have a sense of urgency or use emotions to entice the recipient into clicking a malicious link.

4. Always Keep Your Operating System Up to Date

Keeping your smart devices up to date with the latest security patches is a simple way to avoid botnet attacks. Hackers will often launch botnet attacks that are designed to exploit vulnerabilities in apps and software. 

5. Create Strong, Unique, and Secured Passwords for Every Account

It’s important to take advantage of extra security features such as two-factor authentication and to use a password manager tool to ensure that you have a strong unique password for each account. Google, in partnership with Harris Poll, surveyed that 52% reuse the same password for multiple (but not all) accounts.

6. Practice Cybersecurity Hygiene

The best way to stop future botnet attacks is to be proactive and vigilant. Organizations should provide ongoing cybersecurity awareness training so employees know how to spot potential threats before it’s too late.

Final Thoughts

As botnets have evolved, so have the tools to detect and eradicate them. Today, organizations must layer security measures like:

  • Threat intelligence to help to correlate known threats with activity on your network
  • High-performance malware detection to identify new families and variants of malicious software
  • Post-delivery analysis of emails and automated incident response to contain confirmed email threats

To get further up to speed on everything related to botnets, discover Cyren’s botnet protection services, or download our report on all things malware.


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