Botnet: What it is and how businesses can reduce risk

Overview of a botnet

A botnet is a network of compromised devices that an attacker controls remotely. Each infected device is called a “bot” or “zombie.”

In security conversations, a zombie is a device that has been infected with malware and can receive instructions from a server. The malware usually runs quietly in the background. Users might not notice anything unusual while their devices participate in spam campaigns, credential attacks, or other malicious activity.

This use of the word “bot” is different from the automated tools you may see in other areas of technology. Web crawlers that index sites, automation scripts that call APIs, or tools that collect pricing data are also sometimes called bots. Those tools may be noisy, but they aren’t botnets unless they’re part of a coordinated network of compromised devices under an attacker’s control.

The same applies to “spam bots” or “social bots” on platforms. These bots are automated accounts or scripts, not necessarily infected machines. In simple terms, a botnet is stolen infrastructure: Compromised devices that an attacker can use whenever they choose.

How botnets work

Defending against botnets doesn’t require deep knowledge, but a basic understanding of how they work helps you choose the right controls.

Most botnets follow a similar pattern:

1. Devices are compromised and infected
2. The attacker establishes command and control
3. The botnet is used to run attacks

Compromise and infection

A device becomes part of a botnet when an attacker gains control of it and installs malware. In many cases, this starts with a phishing email.

A typical pattern looks like this:

1. A user receives an email that looks legitimate and appears to come from a trusted brand
2. The message asks the user to open an attachment or click a link
3. When the user does this, malware is downloaded and installed in the background

Command and control

After infection, the attacker needs a way to control the compromised devices. This is the command-and-control layer, often shortened to C2.

Bots usually connect back to one or more servers on a regular schedule. They request instructions, download updates, and upload stolen data. To remain hidden, C2 traffic is often encrypted and blended into normal outbound traffic, for example, by using HTTPS or DNS.

Botnet attacks and monetization

Once the botnet is in place, the attacker can use it for different types of activity.

Common examples include:

• High-volume spam and phishing campaigns
• Malware and ransomware delivery through attachments and links
• Credential theft and credential stuffing

The same botnet can be repurposed over time. It may send spam one week, deliver ransomware the next week, and later be rented to another group. This flexibility is one of the reasons botnets remain a persistent cyberthreat.

How botnets affect your brand

Domain impersonation is already one of the most effective attack methods against enterprises. Botnets make it more dangerous by letting attackers send large volumes of malicious email from many different systems, IP addresses, and locations, which makes these campaigns harder to block and investigate.

A common pattern is to send emails that impersonate your company. The messages may use your logo, your typical tone, and addresses that look like legitimate internal or external communication. If your domain isn’t protected by DMARC, it can be easy for attackers to make a message look like it came from you.

Examples include:

• Fake invoices that appear to come from your finance team
• Banking detail changes that appear to come from procurement
• Password resets or security alerts that appear to come from your IT or security team

In each case, the attacker uses your brand to build trust. The recipient sees a familiar sender name and domain, and is more likely to follow the instructions in the message.

Because botnets often operate from compromised devices that you don’t own, you might only become aware of a problem when a client, partner, or staff member reports fraud, or when there’s visible financial loss or operational impact.

Even if your own inbound email security blocks similar messages, botnet attacks can still damage your reputation. Clients and partners may blame your brand, expect your teams to investigate, or ask for compensation. Over time, repeated incidents like this can weaken confidence in your domain.

How organizations can reduce botnet risk

Enterprises can’t prevent attackers from building or operating botnets. They can, however, reduce two main risks:

1. The risk of their own infrastructure becoming part of a botnet.
2. The risk of botnets sending spoofed emails that abuse their brand.

A practical approach includes several layers.

Strengthen patch and vulnerability management

A disciplined patch process closes many of the easiest paths into your environment. This includes:

• Timely security updates
• Clear prioritization for critical issues

Many botnet operators depend on well-known vulnerabilities that remain unpatched. Reducing the number of exposed and outdated systems lowers the chance that your devices will be compromised.

Monitor for unusual behavior

It is helpful to assume that compromise is possible and to focus on early detection.

Security and IT teams can:

• Use endpoint and network detection tools
• Monitor for unexpected traffic

The goal is to reduce the time that a compromised device remains inside your environment and to limit the impact of any botnet activity that may be running from within.

Protect email and domain identity

Even with strong internal controls, attackers can still use your domain as the visible sender in phishing campaigns. To limit this, you need effective email authentication.

Key steps include:

1. Maintaining accurate Sender Policy Framework (SPF) records that list authorized sending systems
2. Signing outbound email with DomainKeys Identified Mail (DKIM)
3. Publishing and enforcing a DMARC policy

These measures don’t prevent botnets from sending email, but they tell receiving email systems how to handle unauthenticated messages.

How Sendmarc helps reduce brand impersonation

Implementing SPF, DKIM, and DMARC across an enterprise environment can be challenging. Many businesses use multiple domains, a wide range of third-party services, and legacy systems. There is a real risk of disrupting legitimate communication if you change these records without knowing all of your email senders.

Sendmarc helps enterprises move from limited visibility to effective enforcement in a structured and predictable way.

Clear visibility into who’s sending as your domain

Raw DMARC reports are detailed but difficult to work with. Sendmarc processes this data and presents a clear view of:

• Which services and third parties send email as your domains
• Whether those services are passing SPF and DKIM checks

This visibility allows you to separate legitimate senders from potential abuse, including activity that may be driven by botnets.

Having this level of insight also supports internal reporting. Security and IT leaders can quantify how much spoofed traffic is being blocked, show trends over time, and demonstrate progress toward domain protection goals in a way that stakeholders and boards can understand.

Guided configuration of SPF and DKIM

Once you know who’s sending emails on your behalf, the next step is to ensure their messages authenticate correctly.

Sendmarc helps you:

• Configure SPF records without guesswork
• Set up and validate DKIM signing

This reduces the risk of accidental delivery issues and speeds up your path to a stronger DMARC policy.

Safe progression to DMARC enforcement

The end goal should be to reach p=reject. Before you get there, it’s important to make sure that legitimate email flows are protected.

Sendmarc supports this journey by:

1. Helping you move from monitoring (p=none) to quarantine and then to reject in stages
2. Reducing uncertainty around when it’s safe to strengthen policy

When you reach full enforcement, spoofed messages that fail authentication and alignment are far less likely to reach recipients, even if they’re sent from large botnets that you don’t control.

Ongoing monitoring and alerting

Email ecosystems change over time. New tools are added, and attackers adjust their methods.

Sendmarc provides ongoing monitoring so that when a new source begins sending email on behalf of your domain, you can quickly decide whether it’s a legitimate service that needs to be configured or a new attempt at abuse.

Botnets aren’t going away anytime soon, but that’s not the point. For enterprises, the priority is reducing risk and exposure. Strong security hygiene across your environment, combined with DMARC enforcement, makes it far harder for attackers to exploit your systems and impersonate your domain.

With Sendmarc, you can see who’s sending as your domain, fix authentication issues without guesswork, and move safely to DMARC enforcement so that spoofed email is blocked.