How Botnets Work: Inside the Hacker Armies Behind DDoS, Stolen Passwords, and Spam (and How to Stop Them)

If the internet sometimes feels chaotic, there’s a reason. Behind the outage headlines and suspicious login alerts sit botnets—vast armies of hacked devices quietly doing a criminal’s bidding. They’re not just computers anymore. Phones, routers, baby monitors, doorbell cameras—if it connects to the internet, it can be conscripted.

Here’s the unsettling part: you may not notice if your device is drafted. It will keep working, maybe a little slower. Meanwhile, it could be flooding a website with traffic, trying billions of stolen passwords, or sending spam at scale.

The good news? Once you understand how botnets work and how attackers build them, they become much easier to prevent and detect. Let’s pull back the curtain.

What Is a Botnet? The Short Version

A botnet is a network of compromised devices—called “bots” or “zombies”—that a cybercriminal can control remotely as a single unit. That control might be used to:

Overwhelm a site with a Distributed Denial-of-Service (DDoS) attack
Try stolen passwords across many sites (credential stuffing)
Send spam or phishing at scale
Commit ad fraud (clicking and loading ads to fake revenue)
Mine cryptocurrency, proxy traffic, or spread more malware

Think of it like a remote-controlled swarm. One infected device isn’t very powerful. Ten thousand working together can be devastating.

For a quick primer on DDoS specifically, check out Cloudflare’s overview: What is a DDoS attack?

How Botnets Get Built: Infection to Control

Botnets don’t appear out of thin air. Attackers use a repeatable playbook to enroll new devices and keep them under control.

Step 1: Infection

Attackers compromise devices in a few common ways:

Phishing and malicious attachments: A user opens an infected document or installer.
Drive-by downloads: Visiting a compromised site triggers a silent download via a browser exploit.
Exploiting unpatched software: Known vulnerabilities in operating systems, routers, or apps.
Default or weak passwords: Many Internet of Things (IoT) devices ship with factory credentials.
Malicious apps or pirated software: Especially common on phones and PCs without app vetting.
Supply chain weaknesses: Vulnerable libraries or vendor updates.

Here’s why that matters: even simple hygiene—updates, unique passwords, cautious downloads—breaks multiple steps in this chain.

Step 2: Command and Control (C2)

Once a device is infected, it needs instructions. Attackers rely on a Command and Control system to coordinate the swarm. Two patterns dominate:

Centralized C2: Bots phone home to a server or set of servers (often via HTTP/HTTPS or IRC). Easier to build, easier to disrupt.
Peer-to-peer (P2P): Bots share commands among themselves with no single point of failure. Harder to take down, more complex to run.

To stay online, botnet operators also use evasion techniques:

Domain Generation Algorithms (DGA): Malware generates many domain names daily; attackers only need to register a few to maintain control. See Cloudflare’s explainer: DGA-based malware
Fast-flux DNS: Rapidly changing IPs behind a single domain to avoid blocking. Learn more: Fast flux DNS
Encryption and covert channels: Commands hidden inside normal-looking web traffic.

Step 3: Tasking and Monetization

Finally, bots receive instructions:

Start/stop DDoS against a target
Try credential stuffing against a list of sites
Send spam or install additional payloads
Proxy traffic or click ads
Mine cryptocurrency

The operator either profits directly (extortion, crypto) or rents the botnet to others.

The Main Types of Botnet Attacks (With Plain-English Examples)

Let’s break down the work botnets do—and how each attack works at a human level.

DDoS Attacks: Overwhelm by Numbers

DDoS is the best-known use of botnets. Thousands of devices bombard a website or service with traffic until it can’t respond to real users.

Common DDoS flavors: – Volumetric: Sheer bandwidth floods (think: fire hose). – Protocol: Abuse of network protocols (SYN floods, DNS amplification). – Application layer: Target a specific function, like search or login, with realistic-looking requests.

A famous example: In 2016, the Mirai botnet hijacked hundreds of thousands of IoT devices and helped knock major sites offline by overwhelming DNS provider Dyn—affecting Twitter, Netflix, and others. Here’s a readable recap: Wired: The Mirai botnet’s Dyn attack and deeper reporting from KrebsOnSecurity: Mirai coverage.

Why it matters: DDoS is cheap to launch and costly to absorb. Attackers even run “DDoS-for-hire” services. Law enforcement continues to crack down, but the market persists.

Credential Stuffing: Stolen Passwords at Scale

Bots try billions of username/password combos from past data breaches to break into accounts on other sites. Because many people reuse passwords, a small success rate equals lots of compromised accounts.

It’s not a “hack” of your site’s database. It’s abuse of your login page plus recycled passwords.
It’s relentless: attackers rotate IPs, use headless browsers, and mimic real traffic.

For a security deep-dive, OWASP has a useful overview: Credential stuffing

Why it matters: If you reuse passwords, your risk is high—even if your favorite site hasn’t been breached.

Spam and Phishing: Industrial-Scale Deception

Botnets power bulk email campaigns and social media spam. Some even use infected machines to send messages from residential IPs to evade filters.

Infamous examples: – Necurs and Cutwail were among the largest spam botnets before takedowns disrupted them. – Emotet evolved from a banking trojan into a modular spam botnet, later dismantled in a global operation: Europol: Emotet disrupted

Why it matters: Spam is not just annoying—it’s the front door for ransomware, fraud, and more infections.

Ad Fraud and Click Fraud: Faking Traffic for Money

Bots load web pages and click ads to steal advertising dollars. The “3ve” operation used infected machines and fake websites to generate millions in fraudulent ad revenue before being shut down: U.S. DOJ on 3ve case and Google’s summary: Outcome of 3ve

Why it matters: Ad fraud drains budgets, skews analytics, and inflates the perceived reach of campaigns.

Other Monetization: The Gray Market of Access

Cryptomining: Hijacking CPU/GPU power to mine coins.
Proxy-as-a-service: Selling access to your home IP for evading geo-blocking or fraud detection. See DOJ’s takedown of RSOCKS: RSOCKS botnet seized
Initial access brokerage: Selling access to compromised systems to ransomware groups.
Data theft: Harvesting saved credentials or exfiltrating files.

Real-World Botnets in Action

To understand scale and impact, here are a few high-profile cases:

Mirai (IoT): Turned insecure cameras and DVRs into DDoS cannons. It automated scanning for default credentials, then kept evolving into variants. Coverage: Krebs on Mirai.
Emotet (spam/loader): Spread via email, then installed additional malware. Global takedown in 2021. Source: Europol: Emotet.
TrickBot (modular botnet): Pivoted from banking theft to ransomware partnerships. Disrupted by Microsoft and partners in 2020: Microsoft on TrickBot disruption
3ve (ad fraud): A multi-faceted fraud ring using data centers and infected PCs to fake ad traffic. DOJ 3ve.

The lesson: botnets adapt, monetize in multiple ways, and remain a persistent global threat even after major takedowns.

Why IoT Devices Are a Growing Target

Your smart doorbell doesn’t hold sensitive files. So why do attackers care?

Default credentials are common: Many devices ship with “admin/admin.”
Weak or missing updates: Some vendors stop patching quickly, or updates are manual.
Always-on, always-connected: Perfect for constant tasks like DDoS or proxying.
Low visibility: People rarely check logs on a camera or TV.
Exposed services: Telnet/SSH or web interfaces left open to the internet.

Mirai proved how easy it is to mass-scan the internet for devices with default passwords. When thousands of tiny devices work together, they produce serious firepower.

If you build or buy connected devices, OWASP’s IoT resources highlight common pitfalls: OWASP Internet of Things project

How to Protect Your Devices from Being Hijacked

You don’t need to be a security pro. The following actions cut the majority of risk for individuals and small businesses.

For Home Users

Update everything, automatically if possible.
Enable auto-updates on PCs, phones, routers, and IoT devices.
Replace devices that no longer receive security updates.
Use strong, unique passwords everywhere.
A password manager simplifies this. Follow NIST-aligned guidance: NIST SP 800-63B (Passwords)
The FTC has a practical checklist: FTC password tips
Turn on multi-factor authentication (MFA).
Especially for email, banking, cloud storage, and social media.
Lock down your router.
Change default admin credentials.
Disable remote administration unless you truly need it.
Turn off UPnP if you don’t use it. Older US-CERT alert explains the risk: US-CERT on UPnP
Use WPA2/WPA3; avoid WEP.
Segment your network.
Put IoT devices on a separate guest network or VLAN so they can’t reach your laptops and phones.
Use reputable DNS filtering.
Services like Quad9 block known malicious domains by default: Quad9 malware-blocking DNS
Be selective with devices and apps.
Favor vendors with a track record of updates.
Stick to official app stores and be cautious with permissions.
Watch for signs of compromise.
Sudden slowdowns, high data usage, devices running hot, or battery drain.
Unfamiliar processes or apps, or your accounts sending spam.
Unexpected charges or login alerts.

If something feels off, run a reputable antivirus/anti-malware scan on computers and phones. For IoT devices, back up settings, then factory reset and update firmware before reconnecting.

For Small Businesses and Website Owners

Botnets hit companies two ways: your devices get enrolled, or you become the target. Address both.

Harden your perimeter and endpoints.
Patch OS, firmware, VPNs, and internet-facing apps promptly.
Enforce MFA for all administrative access.
Use endpoint protection and EDR on servers and workstations.
Protect your login pages from credential stuffing.
Add MFA and risk-based authentication.
Rate-limit and add bot detection to login endpoints.
Monitor for credential abuse and use breached-password checks. OWASP guidance: Credential stuffing
Deploy a WAF and DDoS protection.
Use a CDN with DDoS mitigation and application-layer protection.
Pre-negotiate with your provider so emergency playbooks exist before an attack.
Monitor and log.
Centralize logs, detect anomalies in traffic, auth failures, and outbound connections.
Keep alerts actionable and test your incident response plan.
Train staff on phishing.
Regular simulations and simple reporting paths reduce risk.

CISA maintains accessible resources for organizations of all sizes: Understanding DDoS attacks (CISA) and broader threat guidance: ENISA Threat Landscape

How to Tell If You’re Part of a Botnet

It’s not always obvious, but here are practical checks:

Network and bandwidth:
Your data usage spikes without explanation.
Router activity lights blink constantly, even when idle.
ISP warns of unusual traffic or abuse complaints.
Device behavior:
Overheating, lag, or battery drain on phones and laptops.
Apps you didn’t install; new extensions in browsers.
Account activity:
Password reset emails you didn’t request.
Logins from odd locations or devices.
Security tools:
Antivirus flags suspicious connections or PUPs.
Your DNS filtering blocks repeated requests to known malicious domains.

What to do next: 1. Disconnect the suspect device from the internet. 2. Back up important data. 3. Run a full malware scan with reputable tools. 4. Update the OS and all apps/firmware. 5. Change passwords—start with email and bank accounts—and enable MFA. 6. For routers and IoT: factory reset, then update, then restore minimal settings with new strong credentials.

If the device is critical or infected repeatedly, consult a professional.

The Botnet Business Model: How Criminals Profit

Understanding the incentives helps you predict what’s next.

Scale above sophistication: Attackers prefer lots of “good enough” devices over a few high-value ones.
Rental markets: Operators rent their botnets to other criminals by the hour or job.
Specialization:
Builders write malware or exploit kits.
Herders run the C2 infrastructure.
Initial access brokers sell footholds.
Affiliates deploy ransomware after buying access.
Evasion as a service: Bulletproof hosting, fast-flux proxies, and DGA-based resilience.

Law enforcement takedowns do work—see Emotet and TrickBot—but the ecosystem is resilient. Disrupting demand (MFA, better patching, stronger fraud controls) reduces the value of botnets over time.

What the Future Holds

A few trends to watch:

More IoT, more targets: The number of connected devices keeps growing faster than secure defaults.
Residential proxying: Expect more “proxy-as-a-service” offerings riding on infected routers and set-top boxes.
Smarter traffic: Botnets will mimic human behavior more convincingly and blend in with normal traffic patterns.
Cloud abuse: Attackers may mix compromised devices with misconfigured cloud resources for added punch.
Better defense: Widespread MFA, passwordless authentication, and behavior-based bot detection will blunt credential stuffing and ad fraud.

Bottom line: This is an arms race—but you can stack the odds in your favor with basic, consistent hygiene.

Quick Checklist: Reduce Your Botnet Risk Today

Turn on automatic updates on everything, including your router.
Replace any device that no longer gets security patches.
Use a password manager and unique passwords; enable MFA everywhere possible.
Put IoT devices on a separate guest network.
Disable remote administration and UPnP unless absolutely needed.
Use a protective DNS service like Quad9 or your security provider’s filter.
Add DDoS protection and bot detection to any site or app you run.
Monitor for abnormal traffic and login behavior.
Check if your emails or passwords have been in known breaches: Have I Been Pwned

Small steps compound. Many botnets take the path of least resistance—don’t be it.

Frequently Asked Questions

What’s the difference between a botnet and a DDoS attack?

A botnet is the army (infected devices). A DDoS attack is one mission the army can be ordered to carry out. Botnets also power credential stuffing, spam, ad fraud, cryptomining, and more.

Can my phone or smart TV really be part of a botnet?

Yes. Any internet-connected device with a vulnerability or default password can be enrolled. Phones get infected via malicious apps or phishing; TVs and cameras often suffer from weak defaults or outdated firmware.

How do botnets avoid being shut down?

Operators use techniques like domain generation algorithms (DGA), fast-flux DNS, encryption, and peer-to-peer communication to make takedowns harder. See DGA-based malware and fast-flux DNS.

Does a VPN protect me from botnets?

A VPN can reduce some network-based risks, but it won’t stop you from installing malware or using a compromised app. Good hygiene (updates, MFA, cautious downloads) matters more.

Are Macs or Linux devices safe from botnets?

All platforms can be targeted. While Windows has historically seen more consumer malware, macOS and Linux systems—including servers and IoT devices—are frequent botnet targets if misconfigured or unpatched.

Is it illegal to stress test my own website with a DDoS tool?

Using “booter/stresser” services often violates laws and terms of service—even if you target your own property—because third-party infrastructure is abused. Work with your hosting provider or a legitimate testing service. For broader context on DDoS, see CISA: Understanding DDoS.

How big are botnets?

Sizes vary from a few thousand devices to hundreds of thousands (or more). IoT botnets often scale quickly because scanning for default credentials is easy and automated.

How can websites defend against credential stuffing?

Use MFA, rate limiting, device fingerprinting, anomaly detection, and breached-password checks. Encourage unique passwords and monitor for spikes in failed logins. OWASP offers guidance: Credential stuffing

What are the signs my router is compromised?

Frequent reboots, changed DNS settings, persistent connectivity issues, or admin passwords that no longer work. If in doubt, factory reset, update firmware, set a strong admin password, and disable unneeded remote features.

Final Takeaway

Botnets thrive on convenience: default passwords, missed updates, and “I’ll do it later.” Flip that script with a few practical habits—automatic updates, unique passwords with MFA, network segmentation for IoT, and basic monitoring—and you dramatically reduce your risk.

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How Botnets Work: Inside the Hacker Armies Behind DDoS, Stolen Passwords, and Spam (and How to Stop Them)

What Is a Botnet? The Short Version