Ransomware: the first 24 hours
How to slow the damage, preserve options, and make recovery decisions without turning an outage into an evidence-destruction exercise.
Scope
For small and midsize organisations facing confirmed encryption, destructive activity, or a credible ransomware note.
Start with the situation, not the slogan
An incident rarely arrives with a neat label. It arrives as a forwarded screenshot, a worried telephone call, or a monitoring alert written by a machine with no sense of occasion. In this case “Ransomware: the first 24 hours” is the working heading, but the label is only a starting hypothesis. The useful work is to establish what happened, what can still happen, and which decision cannot safely wait.
Keep three clocks in view: the attacker’s opportunity, the business interruption, and the lifetime of the evidence. They do not run at the same speed. A hasty change may interrupt access but erase context; a perfect investigation conducted at geological pace may leave the organisation exposed. Good response is the slightly unglamorous art of making the next reversible decision with the best evidence currently available.
Ransomware response is a business continuity problem and an investigation at the same time. Identity, backups, hypervisors, remote management, and cloud services may be affected even when only one endpoint is visibly encrypted.
Composite scenario
How this usually reaches the desk
Imagine the report begins with this observation: “Rapid file renames or encryption, ransom notes, deleted shadow copies, and disabled security tools.” A second check returns another clue: “Mass authentication, remote service creation, administrative share access, or backup-console changes.” Neither fact alone tells the whole story. Together they justify a documented incident, a defined owner, and a deliberate containment decision. This is where a timeline beats a collection of heroic memories; memory is an excellent storyteller and a dreadful audit log.
This scenario combines common operational patterns; it is not presented as a report of one named incident.
What to look for
Begin with preserved, comparable evidence. One signal is rarely proof; use independent observations and a reliable timeline before declaring scope or intent.
Rapid file renames or encryption, ransom notes, deleted shadow copies, and disabled security tools.
Record the exact time, source, identity, system and time zone. Compare it with a known-good baseline and with what the user or service owner expected. A surprising event is a lead, not a conviction.
Mass authentication, remote service creation, administrative share access, or backup-console changes.
Look for the control-plane event that made the visible activity possible: a changed credential, permission, rule, route, token or trusted device. Persistence often looks administrative because, technically, it is.
Unexpected outbound transfers or archive creation that may indicate data theft before encryption.
Correlate the report with independent telemetry before deciding scope. User testimony, identity logs, endpoint evidence and service audit records are strongest when they agree on sequence rather than merely on mood.
Working examples
Run it, read it, decide what changes
These examples use documentation addresses, test identities and bounded targets. Replace placeholders only inside systems you own or are explicitly authorised to operate. Read the expected result and next action before running the command; a successful command is evidence, not yet a conclusion.
Find recently changed files without opening them
- Prerequisites
- A known incident start time and read access to the affected filesystem.
sudo find /srv/data -xdev -type f -newermt "2026-08-18 08:00:00 UTC" -printf '%TY-%Tm-%TdT%TH:%TM:%TSZ %s %p\n' | sort | head -200A time-ordered sample of files modified after the incident start appears.
A burst of renamed or similarly sized files can support the ransomware hypothesis; ordinary batch jobs can look similar. Do not use this list as the only scope measure.
Save the full output, compare with storage snapshots and endpoint telemetry, and identify the first host or account that wrote the files.
Review active SMB sessions
- Prerequisites
- Administrator PowerShell on the file server.
Get-SmbSession |
Sort-Object ClientComputerName |
Select-Object ClientComputerName,ClientUserName,NumOpens,SecondsExistsCurrent SMB clients, users and open-object counts are displayed.
A high open count or new client is a lead, not proof. Terminating the wrong session may interrupt recovery or evidence collection.
Record the list, confirm the suspected source with EDR and file audit logs, then isolate the endpoint or close only the authorised containment target.
Test a restore into an empty directory
- Prerequisites
- A configured repository, its password supplied securely, and an empty destination outside production.
restic snapshots
mkdir -p /restore-test
restic restore latest --target /restore-test
restic check --read-data-subset=5%The restore reports files restored and `restic check` completes without repository errors.
A successful command proves only the sampled repository and selected snapshot were readable. Application consistency and business correctness still need testing.
Open the restored service offline, verify critical records with the owner, record RTO/RPO, and never overwrite encrypted production data during the test.
What to do
Read the whole sequence before starting. Several workstreams may run in parallel, but their evidence, authority and expected outcomes still need to be explicit. Every step below points back to a concrete example; use the example as implementation evidence, not as permission to operate outside the stated scope.
Operational judgement
Containment and recovery are different verbs. Containment limits the next harmful action; recovery returns a service to trustworthy operation. Between them sits eradication: removing the access path and persistence that would make the freshly restored service merely a cleaner target. For Ransomware, Incident response and Recovery, keep those decisions separate in the timeline even if a small team performs them minutes apart.
Communication is also a control. Tell affected people what is known, what remains uncertain, what they must do and when the next update will arrive. Avoid both melodrama and false reassurance. “We are investigating” is useful only when followed by an owner and a time. The goal is to reduce secondary harm without teaching a possible attacker exactly what the team has discovered.
Handover
Make the result useful to the next person
Maintain two views of the incident. The working timeline should contain detailed events, evidence locations, hypotheses and technical actions. The stakeholder update should contain confirmed impact, current containment, material uncertainty, decisions required and the next reporting time. Do not copy speculative indicators into executive statements. Equally, do not polish away uncertainty merely because it looks untidy. Both records should use absolute times with a declared time zone and should identify the source of each important fact.
At shift change, hand over the current scope, trusted administration path, preservation status, active controls, failed actions, business priorities and the next three decisions. Read back the most consequential assumptions. For this case, ensure the record begins with “Activate the incident team and establish an out-of-band communications channel. Assign incident command, technical lead, communications, legal, and evidence ownership.” and does not finish until the team has addressed “Prioritise essential services, validate offline or immutable backups, and recover into a clean environment only after the initial access and persistence paths are understood.” A concise, accurate handover prevents the incoming team from repeating disruptive work or mistaking a quiet telemetry gap for successful containment.
Validate before you close
Recovery is not complete until restored data is tested, privileged access is rebuilt, persistence checks are clean, monitoring is active, and the business owner accepts the remaining risk.
Capture the test, the expected result and the observed result. Where a person or business owner must accept restored service, name them in the record. A green dashboard can confirm that a component is answering; it cannot confirm that invoices, identities or restored data are trustworthy.
Finish with a compact closure note: the original trigger, confirmed scope, evidence retained, controls changed, tests passed, known gaps, residual risk, and the people responsible for the remaining work. Schedule a review while the timeline is still fresh enough to challenge. The purpose is not to find a person to blame; computers already perform blame with admirable efficiency. The purpose is to make the next response faster, safer and less dependent on one person remembering where the useful log was hidden.
Common mistakes
- Resetting systems before preserving volatile evidence and audit logs.
- Treating the first visible symptom as the complete scope of the incident.
- Restoring service without verifying that the attacker’s access path is closed.
These errors usually come from haste, unclear ownership or misplaced confidence. Build the safeguard into the runbook: a required evidence field, a second-person review, a rollback test or a specific exit criterion.
Questions people ask when the clock is running
Does one suspicious event prove compromise?
No. Treat “Rapid file renames or encryption, ransom notes, deleted shadow copies, and disabled security tools.” as a reason to investigate and preserve evidence. Confidence should rise when independent identity, service, endpoint or network records support the same sequence.
Should we reset everything immediately?
Reset or revoke what the evidence and risk justify, but preserve the state you will need to understand the incident. Broad, undocumented resets can interrupt the attacker, the business and the investigation in one impressively efficient stroke.
When can the incident be closed?
Recovery is not complete until restored data is tested, privileged access is rebuilt, persistence checks are clean, monitoring is active, and the business owner accepts the remaining risk. Closure also requires named owners for residual risk and follow-up work; “it seems quiet now” is an observation, not an exit criterion.
Safety boundary
Use these steps only on systems you own or are explicitly authorised to assess. Preserve evidence, follow your organisation’s legal and regulatory obligations, and prefer reversible actions when the situation is not yet understood.
Primary references
- StopRansomware GuideCISA
- Ransomware Protection and ResponseNIST
- SP 800-61 Rev. 3: Incident Response Recommendations and ConsiderationsNIST
- Restic Documentationrestic
Editorial status: first edition. Review the linked vendor documentation for product- and version-specific changes before acting.