In February 2024, Change Healthcare — one of the largest health payment processors in the United States — was hit by the ALPHV/BlackCat ransomware group. The attack disrupted pharmacies, hospitals, and insurance claims across the entire country for weeks. UnitedHealth Group, the parent company, eventually disclosed that the breach affected roughly 100 million individuals and cost the company over $870 million in the first quarter alone. One compromised credential. No multi-factor authentication on a critical remote access portal. That's all it took.

If you're searching for how to prevent ransomware, you're asking the right question. But most guides hand you a checklist and call it a day. I'm going to walk you through what actually works — the specific, layered defenses that security professionals deploy in 2025 to keep ransomware out or contain it when it gets in.

Why Ransomware Is Still the #1 Threat in 2025

According to the FBI's Internet Crime Complaint Center (IC3), ransomware complaints have increased year-over-year since 2019, with critical infrastructure sectors being hit hardest. The 2024 IC3 report logged over 2,825 ransomware complaints — and that only counts what gets reported.

The Verizon 2024 Data Breach Investigations Report found that ransomware or extortion was involved in roughly one-third of all breaches. Threat actors aren't just encrypting files anymore. They're exfiltrating data first, then threatening to leak it. Double extortion is the standard playbook now.

The median ransom payment has climbed. The average cost of a data breach hit $4.88 million globally in 2024, according to IBM's Cost of a Data Breach Report. And paying the ransom doesn't guarantee you'll get your data back — the FBI consistently advises against it.

How to Prevent Ransomware: The Layered Defense Approach

There is no single tool that stops ransomware. I've seen organizations with million-dollar security stacks get compromised because they ignored basic hygiene. Prevention requires layers — each one designed to catch what the previous one missed.

Here's the framework I use when advising organizations on how to prevent ransomware, broken into the categories that matter most.

1. Lock Down the Entry Points

Most ransomware enters through one of three doors: phishing emails, exposed Remote Desktop Protocol (RDP), or unpatched vulnerabilities. CISA's advisories consistently highlight these as the top initial access vectors for ransomware incidents.

Phishing remains the dominant vector. A single employee clicking a malicious link or opening an infected attachment can give a threat actor a foothold in your network. That's why phishing awareness training for your organization isn't optional — it's your first defensive layer.

RDP exposure is the one that frustrates me most because it's entirely preventable. If you have RDP open to the internet, shut it down today. Use a VPN with multi-factor authentication, or better yet, move to a zero trust network access (ZTNA) solution.

Unpatched systems are essentially open invitations. The Cl0p ransomware group's mass exploitation of the MOVEit Transfer vulnerability in 2023 showed what happens when organizations delay patching. Thousands of organizations were compromised through a single known vulnerability.

2. Deploy Multi-Factor Authentication Everywhere

The Change Healthcare breach happened because a Citrix remote access portal lacked multi-factor authentication. One set of stolen credentials gave the attacker direct access.

MFA should be enforced on every remote access system, every email account, every admin console, and every cloud service. Period. Passwords alone haven't been sufficient for years. In my experience, MFA blocks over 99% of credential-based attacks when properly implemented.

Use phishing-resistant MFA where possible — FIDO2 security keys or passkeys. SMS-based MFA is better than nothing, but SIM-swapping attacks have weakened its reliability.

3. Train Your People Like Their Jobs Depend on It

Because they do. The Verizon DBIR consistently shows that the human element is involved in the majority of breaches. Social engineering and credential theft are the techniques threat actors rely on most.

Security awareness training isn't a once-a-year compliance checkbox. It should be ongoing, scenario-based, and reinforced with regular phishing simulations. When employees can recognize a suspicious email, a pretexting phone call, or a fake login page, your entire attack surface shrinks.

I recommend starting with a structured cybersecurity awareness training program that covers ransomware, phishing, social engineering, and credential hygiene. Then layer in quarterly phishing simulations to measure and improve real-world behavior.

4. Implement the Principle of Least Privilege

When ransomware lands on one machine, the damage it can do depends entirely on what that machine — and that user account — can access. If your helpdesk staff have domain admin rights, you've already lost.

Audit your Active Directory. Remove unnecessary admin privileges. Segment your network so that a compromise in accounting can't reach your backup servers. This is the core of a zero trust architecture: never trust, always verify, and limit blast radius.

Specifically, I recommend these steps:

  • Separate admin accounts from daily-use accounts — no one should browse email with domain admin credentials.
  • Use privileged access management (PAM) tools to vault and rotate admin passwords.
  • Implement network segmentation between business units and between operational technology and IT systems.
  • Restrict lateral movement with host-based firewalls and microsegmentation.

5. Build a Backup Strategy That Actually Survives Ransomware

I've worked incidents where the organization had backups — but the ransomware encrypted those too. Your backup strategy has to be designed with a malicious adversary in mind.

Follow the 3-2-1-1 rule:

  • 3 copies of your data.
  • 2 different storage media types.
  • 1 copy offsite.
  • 1 copy offline or immutable.

That last point is critical. Immutable backups — ones that cannot be modified or deleted for a set retention period — are your insurance policy. Cloud providers like AWS (S3 Object Lock) and Azure (immutable blob storage) offer this natively.

Test your restores regularly. A backup you've never tested is just a hope, not a plan.

6. Patch Fast, Patch Consistently

CISA maintains its Known Exploited Vulnerabilities (KEV) catalog, which lists vulnerabilities actively used by threat actors in the wild. If a vulnerability appears on that list and exists in your environment, treat it as a P1 emergency.

Establish a patching cadence: critical and actively-exploited vulnerabilities within 48 hours, high-severity within two weeks, and everything else within 30 days. Automate where you can. The organizations I've seen get hit almost always have a patching gap measured in months, not days.

7. Use Endpoint Detection and Response (EDR)

Traditional antivirus is not enough. Modern ransomware uses living-off-the-land techniques — legitimate system tools like PowerShell, WMI, and PsExec — to evade signature-based detection.

EDR solutions monitor behavior on endpoints, detect suspicious activity chains, and can automatically isolate a compromised machine before ransomware spreads. Deploy EDR on every endpoint — workstations, servers, and especially domain controllers.

Make sure your security team or managed detection and response (MDR) provider is actually monitoring the alerts. I've seen EDR tools fire alerts that sat unread for days while ransomware propagated across an entire domain.

What to Do When Ransomware Gets Through Anyway

Prevention isn't perfect. You need a tested incident response plan. Here's what yours should include:

  • Isolation procedures: How to quickly disconnect affected systems from the network without pulling the plug on everything.
  • Communication plan: Who calls legal, who notifies leadership, who contacts your cyber insurance carrier.
  • Forensic preservation: How to capture evidence before you start recovery. This matters for law enforcement and insurance claims.
  • Recovery playbook: Step-by-step restore procedures from your tested immutable backups.
  • Regulatory notification: Timelines for notifying affected individuals and regulators. HIPAA, state breach notification laws, SEC rules — know your obligations before the incident.

Run a tabletop exercise at least twice a year. Put your leadership team in the room and walk through a realistic ransomware scenario. The time to figure out your response process is not during the actual attack.

What Is the Single Most Effective Way to Prevent Ransomware?

If I had to pick one control, it would be multi-factor authentication on all remote access combined with ongoing security awareness training. Those two controls together address the vast majority of initial access techniques used by ransomware operators today. MFA stops credential theft from being useful. Training stops phishing from being effective. Together, they close the two biggest doors that threat actors walk through.

But one control is never enough. The organizations that avoid ransomware in 2025 are the ones running layered defenses — patching, segmentation, EDR, immutable backups, and a trained workforce — all working together.

The $4.88M Lesson Most Organizations Learn Too Late

Every ransomware victim I've worked with said some version of the same thing: "We knew we should have done this sooner." The patches were available. The MFA option existed. The phishing training was on someone's roadmap but never got prioritized.

Ransomware defense isn't about buying the most expensive tool. It's about doing the fundamentals consistently. Patch your systems. Enforce MFA. Segment your network. Back up your data immutably. And train your people — because they are both your biggest vulnerability and your strongest defense.

Start now. Get your team enrolled in cybersecurity awareness training and run phishing simulations that measure real behavior change. The cost of preparation is a fraction of the cost of recovery.

A Quick-Reference Ransomware Prevention Checklist

  • Enforce multi-factor authentication on all remote access, email, cloud services, and admin accounts.
  • Deploy and monitor endpoint detection and response (EDR) on all systems.
  • Maintain immutable, offsite backups — test restores quarterly.
  • Patch critical and actively-exploited vulnerabilities within 48 hours.
  • Conduct ongoing security awareness training with regular phishing simulations.
  • Implement least-privilege access and network segmentation.
  • Disable unnecessary RDP and restrict remote access through VPN or ZTNA.
  • Maintain and test your incident response plan with tabletop exercises twice a year.
  • Monitor the CISA StopRansomware advisories for current threat intelligence.
  • Review and enforce email security controls: SPF, DKIM, DMARC, and attachment sandboxing.

Ransomware isn't going away. But with the right defenses in place, your organization doesn't have to be the next headline.