Ransomware encryption can be a late stage of an intrusion. A detection program that correlates earlier identity, endpoint, network, and data-protection activity may give responders a chance to investigate or contain the intrusion before files are encrypted—but no fixed warning window or guaranteed outcome is established.
Why the encryption event may come late
A ransom note or sudden burst of file changes can be an unmistakable signal, but it may arrive after an intruder has already gained access, explored the environment, weakened defenses, or prepared data for transfer. CISA warns that a ransomware infection can indicate a previous, unresolved compromise and advises investigating earlier activity and possible precursor malware in its #StopRansomware Guide.
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That makes pre-encryption detection a search for suspicious behavior across a possible intrusion—not a hunt for one universal ransomware signature. The sequence varies: activity can be skipped, repeated, or carried out in a different order, and a single event such as an administrator changing a setting may be legitimate. Correlation and context matter.
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What to look for before encryption
The following map combines CISA’s general ransomware hunting guidance with examples in the CISA/FBI advisory about Play ransomware. Play-specific observations are identified as such; they should not be treated as a template for every ransomware incident. The advisory’s ATT&CK mapping uses Enterprise version 17 and was updated June 4, 2025. See the CISA/FBI Play Ransomware advisory.
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| Activity to investigate | Signals and context | Telemetry to correlate |
|---|---|---|
| Access and account abuse | Unexpected VPN logins, unusual privileged-account activity, or newly created or escalated accounts. These are investigation leads, not proof of compromise. | Identity-provider and VPN authentication records; account and privilege changes; endpoint and network activity associated with the account. CISA’s general guide discusses suspicious accounts and VPN activity. |
| Discovery and privilege activity | Unexpected software, services, or scheduled tasks, especially when they appear alongside unusual account or host activity. The Play advisory documents discovery and defense-evasion behavior specific to that actor. | Endpoint process and configuration events; service and task creation; identity events; connections to and from the affected host. |
| Defense and recovery impairment | Changes affecting endpoint protection, backup systems, shadow copies, disk journaling, boot configuration, or cloud data-protection resources. | Endpoint security and configuration logs; backup and storage administration events; cloud IAM, network-security, and data-protection changes. CISA recommends detecting and preventing changes to cloud control resources in its general guide. |
| Lateral movement and staging | Unusual host-to-host connections, unexpected services or tasks, and software appearing outside normal change activity. Assess these with the host and account context rather than by tool name alone. | Endpoint events, network connections, identity activity, and change records. CISA’s guide and the Play advisory provide broader and actor-specific examples, respectively. |
| Possible data exfiltration | Abnormal outbound transfers or unexpected use of file-transfer and cloud-storage services. CISA’s guide names Rclone, Rsync, web-based storage, and FTP/SFTP as examples; the Play advisory describes WinRAR staging and WinSCP transfer. These tools also have legitimate uses. | Network connection and transfer-volume records; endpoint process context; proxy, firewall, or relevant cloud-service logs. Compare activity with the account, host, destination, and expected business use. |
| Encryption activity | Unusual bursts of file modification, ransom notes, or known ransomware artifacts. These can be valuable signals, but may indicate the intrusion is already at a late stage. | Endpoint file and process telemetry, supported by host, user, and network context. |
Collect the telemetry needed to connect the stages
A detection is only as useful as the events it can observe. Central collection helps analysts correlate what happened to an account with what happened on its devices and across the network; missing or short-lived logs can leave those events disconnected. CISA recommends centralized logging, endpoint controls, behavioral analytics, and centrally monitored intrusion detection systems (IDS) for command-and-control (C2) and other potentially malicious network activity before ransomware deployment.
- Identity and remote access: retain authentication, VPN, account creation, and privilege-change events with timestamps and user or service identities.
- Endpoints: collect security alerts and relevant process, configuration, file, service, and scheduled-task activity. Endpoint detection and response (EDR) is among the endpoint controls CISA recommends.
- Network: monitor relevant connections and outbound activity, including enough context to relate a connection to a device and, where available, a process or user. IDS monitoring can help surface C2 or other suspicious network behavior before deployment.
- Backups, storage, and cloud controls: make administrative and protection-setting changes visible, including changes to cloud IAM, network security, and data-protection resources.
- Central retention and correlation: route relevant events to a monitored, centrally accessible location and retain them long enough for investigation under your organization’s policies.
Network indicators such as domains, IP addresses, or protocol patterns can help investigate a particular campaign, but they can change and should not carry the detection strategy alone. Behavioral context—who acted, on which host, and what changed around the same time—is more useful for deciding whether an event needs investigation.
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Build and validate detections as an operational loop
CISA and the FBI recommend validating security controls against mapped threat behaviors, analyzing detection and prevention performance, and tuning the people, processes, and technologies involved. Apply that guidance as a repeatable workflow:
- Choose a behavior and define its context. Specify what you want to detect—for example, an unexpected change to a backup control—and what makes it suspicious in your environment.
- Confirm the data exists. Identify the event sources, fields, central collection path, and retention needed to see the behavior and connect it to related activity. Record gaps before relying on the alert.
- Write for an investigation, not just a match. Include useful context such as the user or service account, affected host, event time, relevant changes, and linked activity when the telemetry supports it. Define who receives the alert and what initial review or escalation it should prompt.
- Exercise the behavior safely. Use an approved test method appropriate to the environment. Confirm that the expected event is collected, the alert is generated and routed, and its context is sufficient for a responder to act.
- Review results and tune. Record what was detected, what was missed, alert noise, telemetry gaps, and response friction. Adjust the logic or collection, then test again.
A mapped technique or a rule that has been written is not evidence of successful detection. Performance claims require actual validation in the relevant environment; the CISA/FBI guidance supports testing and tuning, but does not establish a general pre-encryption detection rate or lead time.
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Make the alert actionable—and protect recovery
When a signal fires, responders need an accountable owner, enough context to assess related activity, and an approved way to escalate and contain. Preserve relevant logs and evidence, and follow the organization’s incident-response process when deciding how to contain affected accounts or systems; a poorly scoped action can disrupt legitimate operations or complicate investigation.
Detection is only one part of limiting impact. CISA also recommends protected, resilient backups and recovery planning. Monitor for attempts to impair those safeguards, and maintain recovery options that are not easily altered by the same compromised accounts or systems. If prevention or early response fails, recovery readiness can still reduce the damage.
What this approach can—and cannot—promise
Correlating earlier activity can create an opportunity to investigate or contain an intrusion before encryption, but the available guidance does not establish how much warning any organization will receive, how often a detection will succeed, or that encryption can always be stopped. Coverage depends on the behavior, available telemetry, alert quality, and the ability of people and processes to respond in time. Treat actor advisories as useful examples to inform detection engineering, not universal signatures or a complete map of every ransomware operation.
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