Ransomware explained: The complete 2025 defense guide

The ransomware landscape in 2025 has reached unprecedented scale and sophistication. With 85 active ransomware groups operating simultaneously and damages projected at $57 billion globally, organizations face a threat environment that demands both technical depth and strategic clarity. This guide provides security professionals with current intelligence on how ransomware works, which threat actors pose the greatest risk, and what defensive measures actually reduce exposure.

Whether you are building detection capabilities, refining incident response procedures, or briefing leadership on organizational risk, the information here reflects the latest threat research and defensive best practices from authoritative sources including the FBI, CISA, and MITRE ATT&CK.

What is ransomware?

Ransomware is a type of malicious software that encrypts files on a victim's device or network and demands a ransom payment — typically in cryptocurrency — to restore access. According to the FBI, ransomware prevents access to computer files, systems, or networks until payment is made.

CISA characterizes ransomware as "an ever-evolving form of malware designed to encrypt files on a device, rendering any files and the systems that rely on them unusable." This definition captures the operational reality security teams face: ransomware does not simply lock data but disrupts the business processes that depend on that data.

The financial impact of ransomware in 2025 is staggering. According to Cybersecurity Ventures, global ransomware damages reached $57 billion this year — approximately $156 million per day. These costs extend far beyond ransom payments to include business disruption, recovery expenses, reputational damage, and regulatory penalties.

What makes ransomware particularly concerning is its evolution from a nuisance into a sophisticated criminal enterprise. Modern ransomware operators conduct reconnaissance, establish persistence, and exfiltrate sensitive data before ever deploying encryption. This transforms each ransomware incident into a potential data breach with long-term consequences for affected organizations.

How ransomware differs from other malware

Ransomware belongs to the broader category of malware — malicious software designed to harm computer systems or their users. However, ransomware possesses unique characteristics that distinguish it from other malware types.

Unlike viruses that spread and corrupt files, trojans that provide backdoor access, or spyware that exfiltrates information quietly, ransomware announces itself. The cyberattack becomes visible to victims through ransom notes demanding payment. This visibility serves the attackers' financial motivation: victims cannot pay for something they do not know has happened.

The financial motivation also drives ransomware's rapid evolution. Attackers continually refine their techniques to maximize payment rates and minimize detection, creating an arms race between offensive innovation and defensive capability.

How ransomware works

Modern ransomware attacks follow a predictable sequence that defenders can disrupt at multiple stages. Understanding this attack chain enables security teams to implement layered defenses and detect intrusions before encryption occurs.

The typical ransomware attack progresses through five stages:

1. Initial access — attackers gain entry through phishing, compromised credentials, or exploited vulnerabilities
2. Lateral movement — malware spreads across the network while harvesting additional credentials
3. Privilege escalation — attackers obtain administrative access to maximize impact
4. Data exfiltration — sensitive information is stolen before encryption for double extortion leverage
5. Encryption and ransom demand — files are encrypted and victims receive payment instructions

Each stage offers detection and disruption opportunities. Organizations that focus exclusively on preventing initial access miss chances to catch attackers during the often lengthy period between compromise and encryption.

Initial access vectors in 2025

The entry points ransomware operators use have shifted significantly. According to HIPAA Journal, compromised VPN credentials accounted for 48% of ransomware attacks in Q3 2025, up from 38% in Q2. This represents a fundamental change from earlier years when phishing dominated initial access.

The shift toward credential-based initial access reflects both the widespread availability of stolen credentials on criminal marketplaces and the effectiveness of initial access brokers — specialists who compromise systems and sell access to ransomware operators. These brokers often use infostealers to harvest credentials at scale.

External service exploitation remains significant, with recent campaigns targeting vulnerabilities in VPN appliances (CVE-2024-40766 in SonicWall), Citrix NetScaler devices (CVE-2025-5777), and enterprise software like Oracle E-Business Suite (CVE-2025-61882).

Lateral movement and data exfiltration

Once inside a network, ransomware operators move quickly. According to Vectra AI research on lateral movement, average lateral movement occurs within 48 minutes of initial compromise. The fastest observed cases show attackers achieving full network propagation in just 18 minutes.

This speed creates a narrow window for detection and response. Attackers use legitimate administrative tools and credentials to move laterally, making their activity difficult to distinguish from normal network operations without behavioral analysis.

Data exfiltration has become nearly universal in ransomware attacks. According to Deepstrike, 76% of 2025 ransomware attacks involved data exfiltration prior to encryption. This enables double extortion — even if victims restore from backups, attackers threaten to publish stolen data.

Common tools observed in the exfiltration phase include:

• Rclone and Rsync for cloud storage transfers
• Cobalt Strike for command and control
• Mimikatz for credential harvesting
• FTP/SFTP for bulk data transfer

MITRE ATT&CK mapping

The MITRE ATT&CK framework provides a standardized vocabulary for describing ransomware techniques. The primary technique for ransomware is T1486 - Data Encrypted for Impact, categorized under the Impact tactic.

The ATT&CK framework documents over 70 ransomware families with their associated techniques. Security teams can use this mapping to validate detection coverage and identify gaps in their defensive capabilities through proactive threat hunting.

Types of ransomware

Ransomware has evolved from simple encryption tools into sophisticated multi-faceted threats. Understanding the major variants helps defenders anticipate attack patterns and prepare appropriate responses.

Crypto-ransomware vs locker ransomware

The fundamental distinction in ransomware types is between crypto-ransomware and locker ransomware.

Crypto-ransomware (also called encrypting ransomware) encrypts individual files and data on infected devices. According to Keeper Security, victims can still use their devices but cannot access encrypted files without the decryption key. Modern crypto-ransomware uses strong encryption algorithms including AES-256, ChaCha20, and RSA-2048 that are computationally infeasible to break.

Locker ransomware (screen lockers) takes a different approach — locking users out of their entire systems rather than encrypting individual files. According to Check Point, locker variants prevent any access to the device until payment is made. While locker ransomware was more common in ransomware's early history, crypto-ransomware dominates today due to its greater impact and harder recovery path.

Multi-extortion ransomware

Modern ransomware has evolved beyond simple encryption into multi-layered extortion schemes.

Double extortion ransomware combines data encryption with data theft. Attackers first exfiltrate sensitive information, then encrypt systems. If victims restore from backups without paying, attackers threaten to publish or sell the stolen data. According to Arctic Wolf, 96% of ransomware incident response cases in 2025 involved data exfiltration — making double extortion the norm rather than the exception.

Triple extortion ransomware adds additional pressure tactics beyond encryption and data theft. These may include:

• Threatening to contact the victim's customers, partners, or patients about the breach
• Launching DDoS attacks against the victim's infrastructure
• Targeting third parties with extortion demands based on stolen data

This evolution means ransomware attacks now create multiple, overlapping harms — operational disruption from encryption, data breach notification requirements from exfiltration, and reputational damage from public leak threats.

Ransomware-as-a-Service (RaaS)

The industrialization of ransomware has transformed it from a technical crime into an accessible business model. According to IBM, ransomware-as-a-service (RaaS) is a business model where ransomware developers sell or lease their malware to affiliates who conduct the actual attacks.

RaaS operators provide affiliates with:

• Ready-to-deploy ransomware payloads
• Administrative panels for victim management
• Payment processing infrastructure
• Negotiation support and victim communication tools
• Technical support and updates

In exchange, affiliates share ransom proceeds with the RaaS operators. According to Flashpoint, typical affiliate revenue shares range from 70–85% of ransom payments, with Qilin offering an industry-leading 85% share to attract affiliates.

This model dramatically lowers barriers to entry. Technically unsophisticated criminals can conduct sophisticated attacks using professional-grade tools, expanding the threat landscape and increasing attack volume.

Ransomware in practice: 2025 threat landscape

The 2025 ransomware ecosystem is characterized by fragmentation, sophistication, and record attack volumes. Security teams need current intelligence on active threat actors and their tactics to prioritize defenses effectively.

According to Check Point Research, Q3 2025 saw a record 85 active ransomware groups operating simultaneously — the highest number ever observed. This fragmentation follows law enforcement disruptions of major groups and reflects the ease with which new groups can launch using RaaS infrastructure.

Attack volume increased substantially, with 4,701 ransomware incidents recorded globally between January and September 2025, representing a 46% increase over the same period in 2024.

Most active ransomware groups in 2025

Qilin emerged as the dominant ransomware group in 2025, processing over 75 victims monthly by Q3. The group's 85% affiliate revenue share — higher than competitors — has attracted skilled affiliates from disbanded operations. Notably, North Korean threat actors deployed Qilin payloads in March 2025, indicating nation-state collaboration with criminal ransomware operations.

Akira accumulated $244.17 million in proceeds as of late September 2025, according to CISA advisories. The group targets SMBs and critical infrastructure across manufacturing, education, IT, healthcare, and financial services.

LockBit re-emerged with version 5.0 in September 2025 despite significant law enforcement pressure including Operation Cronos. While diminished from its peak, the group's persistence demonstrates the resilience of well-established RaaS operations.

High-profile case studies

Change Healthcare (2024–2025): The ALPHV/BlackCat attack on Change Healthcare represents the largest healthcare data breach in U.S. history. According to AHA, approximately 192.7 million individuals were affected, with total costs estimated at $3 billion. The root cause was compromised credentials for a Citrix server without multi-factor authentication — a basic security control failure with catastrophic consequences.

Qilin "Korean Leaks" Campaign (September 2025): According to The Hacker News, Qilin compromised a single managed service provider (GJTec) and used that access to attack 28 downstream organizations, including 24 in South Korea's financial sector. Over 1 million files and 2TB of data were exfiltrated. This supply chain attack demonstrates how MSP compromises can amplify ransomware impact exponentially.

Clop Oracle EBS Campaign (November 2025): According to Z2Data, the Clop ransomware group exploited CVE-2025-61882 (CVSS 9.8) in Oracle E-Business Suite to compromise over 100 companies including Broadcom, Estee Lauder, Mazda, Canon, Allianz UK, and the Washington Post. The campaign demonstrated Clop's continuing pattern of mass exploitation following similar MOVEit attacks in 2023.

Industry impact statistics

Ransomware targeting varies significantly by sector. According to Industrial Cyber, critical infrastructure sectors accounted for half of all 2025 ransomware attacks.

SMBs face disproportionate impact. According to Verizon DBIR analysis, 88% of data breaches at SMBs involve ransomware (compared to 39% for large organizations), and 60% of attacked small businesses close within six months. The lack of dedicated security resources and incident response capabilities makes smaller organizations particularly vulnerable.

Detecting and preventing ransomware

Effective ransomware defense requires layered controls spanning prevention, detection, and response. While prevention remains the most cost-effective approach, organizations must also prepare to detect attacks in progress and respond effectively when defenses fail.

Prevention best practices

CISA's #StopRansomware Guide provides authoritative prevention guidance that security teams should implement as baseline controls:

Priority actions (implement immediately):

1. Prioritize remediating known exploited vulnerabilities — focus on CISA KEV catalog entries
2. Enable and enforce phishing-resistant multi-factor authentication on all external-facing services
3. Maintain regular offline, encrypted backups and test restoration procedures

Additional technical controls:

• Implement zero trust architecture principles for network access
• Segment networks to limit lateral movement opportunities
• Disable SMBv1 and upgrade to SMBv3 with encryption
• Centralize logging with SIEM and minimum 12-month retention
• Restrict PowerShell execution via group policy
• Deploy EDR, NDR, or XDR solutions with real-time detection capabilities
• Enforce passwords of at least 15 characters
• Separate administrative accounts from daily-use accounts
• Reduce attack surface by disabling unnecessary services

Given that 48% of 2025 attacks used compromised VPN credentials, organizations should audit VPN configurations, implement MFA on all remote access, and consider zero-trust network access alternatives.

Backup strategy for ransomware resilience

The modern 3-2-1-1-0 backup rule, as detailed by Veeam, provides ransomware-resilient data protection:

• 3 copies of data (primary plus two backups)
• 2 different storage media types
• 1 copy offsite
• 1 copy immutable or air-gapped
• 0 errors after verification testing

Immutable storage converts backups to write-once, read-many (WORM) format that cannot be overwritten, changed, or deleted — even by administrators with full credentials. This protects against ransomware that specifically targets backup systems.

Regular backup testing is critical. Organizations should verify restoration procedures at least quarterly and document realistic recovery time objectives based on actual test results.

Detection indicators and network monitoring

Detection opportunities exist throughout the ransomware attack chain. Network detection and response solutions provide visibility into attacker behaviors that endpoint tools may miss.

Precursor malware to monitor:

• Bumblebee, Dridex, Emotet, QakBot, and Anchor loaders often precede ransomware deployment
• Detection of these threats should trigger immediate investigation

Network indicators of ransomware activity:

• Abnormal data outbound on any port (exfiltration)
• Tools like Rclone, Rsync, FTP/SFTP moving large data volumes
• Command and control callbacks to unknown infrastructure
• Lateral movement patterns (unusual authentication, service account abuse)
• DNS tunneling attempts
• ARP spoofing activity

Behavioral baselines enable detection of anomalies. When users or systems deviate from established patterns — accessing unusual resources, authenticating at unusual times, or transferring unusual data volumes — these deviations warrant investigation.

Incident response first steps

If your organization is hit by ransomware, CISA provides immediate response guidance:

1. Isolate immediately — disconnect affected systems from the network to prevent spread
2. Do NOT restart or reboot — this may trigger additional harm or destroy forensic evidence
3. Secure backups — disconnect backup systems to prevent encryption
4. Document everything — screenshot ransom notes and preserve system state
5. Assess scope — determine which systems are affected and the extent of encryption
6. Contact authorities — notify FBI, CISA, and local law enforcement
7. Check for free decryptors — the No More Ransom Project provides free decryption tools for 100+ ransomware families

Activating your incident response plan early improves outcomes. Organizations with tested response procedures recover faster and minimize damage.

Recovery times have improved significantly. According to Sophos, 56% of organizations recovered within one week in 2025, compared to 33% in 2024. This improvement reflects better backup practices and more mature incident response capabilities across the industry.

Should you pay the ransom?

The FBI and CISA recommend against paying ransoms. The data supports this position:

• Only 46% of organizations that pay ransoms successfully recover their data (CSO Online)
• 93% of paying victims still had their data stolen and potentially exposed
• Approximately 80% of organizations that paid experienced subsequent attacks
• Payment funds criminal enterprises and incentivizes future attacks

Victim behavior reflects this guidance. According to Sophos, 63% of ransomware victims refused to pay in 2025, up from 59% in 2024. Meanwhile, 97% of organizations successfully recovered their data through backups or other means — demonstrating that payment is not necessary for recovery.

If you are considering payment, legal counsel and law enforcement engagement should precede any decision. Some payments may violate sanctions regulations, and authorities may have intelligence about the specific threat actor that affects the decision.

Ransomware and compliance

Regulatory frameworks increasingly mandate ransomware-specific controls and reporting requirements. Security teams must understand compliance obligations and map existing controls to framework requirements.

Framework mapping

NIST IR 8374 - Ransomware Risk Management Profile: This NIST publication applies the Cybersecurity Framework's five core functions (Identify, Protect, Detect, Respond, Recover) specifically to ransomware risk. Updated for CSF 2.0 in January 2025, it provides actionable guidance aligned with ISO/IEC 27001:2013 and NIST SP 800-53 Rev. 5.

MITRE ATT&CK Framework: Version 18 of ATT&CK (October 2025) documents over 70 ransomware families and their techniques. Organizations can use ATT&CK to validate detection coverage against known ransomware behaviors and identify capability gaps.

NIS2 Directive (EU): The NIS2 Directive requires essential and important entities across 18 critical sectors to implement ransomware-specific controls. Key requirements include 24-hour early warning for significant incidents and penalties up to EUR 10 million or 2% of global revenue for non-compliance.

Cyber insurance trends

Ransomware significantly affects cyber insurance markets. According to Resilience, the average ransomware insurance claim reached $1.18 million in 2025 — a 17% increase year-over-year. Ransomware accounts for 76% of incurred losses despite representing 56% of claims.

Coverage challenges are increasing. According to HIPAA Journal, approximately 40% of cyber insurance claims were denied in 2024, often due to "failure to maintain security" exclusions. Insurers are scrutinizing vulnerability management practices, MFA deployment, and backup procedures when evaluating claims.

An emerging concern: the Interlock ransomware group has been observed stealing cyber insurance policies from victims to benchmark ransom demands against coverage limits. This intelligence-driven approach to ransom pricing makes adequate coverage a potential liability without corresponding security improvements.

Modern approaches to ransomware defense

The ransomware landscape demands continuous evolution in defensive strategies. As attackers develop new techniques — EDR killers, cloud security threats like Codefinger's AWS SSE-C exploitation, and nation-state collaboration — defenders must adapt detection and response capabilities accordingly.

Network-based detection has become critical as attackers increasingly evade endpoint controls. NDR solutions provide visibility into lateral movement, data exfiltration, and command and control communications that endpoint tools cannot see.

Extended detection and response (XDR) platforms correlate signals across endpoint, network, cloud, and identity data sources. This cross-layer visibility reduces false positives and accelerates investigation by connecting related activities across the environment.

Zero trust architecture adoption continues to grow as organizations recognize that perimeter-based security cannot protect against credential-based attacks. When 48% of ransomware incidents begin with compromised credentials, assuming the network is already compromised and validating every access request becomes essential.

How Vectra AI thinks about ransomware

Vectra AI approaches ransomware defense through Attack Signal Intelligence — focusing on detecting attacker behaviors across the entire attack chain rather than relying solely on signatures or known indicators. By analyzing network traffic, cloud activity, and identity signals, the platform identifies lateral movement, privilege escalation, and data exfiltration patterns that precede ransomware deployment.

The "Assume Compromise" philosophy recognizes that determined attackers will eventually bypass preventive controls. The critical capability is finding attackers during the window between initial access and encryption — often as little as 18 minutes, but typically long enough for behavioral threat detection to identify malicious activity.

AI security capabilities enable detection of novel ransomware behaviors without prior knowledge of specific variants. When attackers develop new evasion techniques, behavioral analysis continues to identify the underlying attack patterns — credential abuse, unusual data access, lateral connection attempts — that remain consistent across campaigns.

Conclusion

Ransomware in 2025 represents a mature, sophisticated, and highly fragmented threat that no organization can afford to ignore. With 85 active groups, $57 billion in global damages, and attacks that routinely combine encryption with data theft, the stakes have never been higher.

The data shows that prevention and preparation work. Organizations that implement MFA, maintain tested immutable backups, and segment their networks recover faster and avoid paying ransoms. Those that invest in detection capabilities — particularly network-based behavioral analysis — catch attackers before encryption begins.

The path forward requires continuous evolution. As ransomware operators develop new techniques and exploit new vulnerabilities, defenders must adapt. Regular testing of detection coverage against the MITRE ATT&CK framework, ongoing security awareness training, and quarterly backup restoration tests provide the foundation for resilient operations.

For organizations seeking to strengthen their ransomware defenses, Vectra AI's approach to Attack Signal Intelligence provides detection across the entire attack chain — identifying the behaviors that precede ransomware deployment regardless of specific malware variants or evasion techniques.