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If you suspect someone has accessed your small business’s systems, isolate affected devices from the network, coordinate decisions through a business lead, and contact qualified incident-response help. Don’t shut a device down unless responders direct you to or it cannot otherwise be disconnected: power loss can erase volatile evidence. A post-intrusion assessment should establish how access happened, what systems and data may be affected, whether the attacker still has access, and what must change before recovery.
What to do first after a suspected intrusion
Use your incident-response plan if you have one. Choose a business lead to coordinate technical, operational, communications, and legal decisions; uncoordinated actions can disrupt operations or alert an attacker. If compromised systems may be monitored, use an appropriate out-of-band channel to coordinate rather than relying on them.
- Isolate affected systems from the network. Disconnect affected endpoints or systems where you can do so safely, and coordinate the action across the business. If you cannot disconnect a device any other way, powering it down may be a fallback, but it can destroy volatile evidence. Follow a qualified responder’s direction when available. CISA’s #StopRansomware Guide explains these evidence and containment considerations.
- Preserve what may disappear. Avoid unnecessary changes to affected machines. System memory, Windows Security logs, and firewall log buffers may be volatile or retained only briefly. Ask responders how to preserve them; do not attempt memory capture or forensic imaging without qualified help.
- Keep a simple incident record. Record what you observed, when it was noticed, which systems appear affected, and the containment steps taken. Preserve relevant alerts and communications, and tell responders what has already been changed. Do not claim that data was or was not accessed before evidence supports that conclusion.
- Protect essential operations. Identify critical services and prioritize continuity and safe restoration with your response team. Do not reconnect or restore a potentially compromised system just to get it working again.
The FTC’s business data-breach guide advises against misleading public statements and against withholding key information people need to protect themselves. Coordinate any external communication with the response team and counsel.
What a post-intrusion assessment should establish
A cleanup alone is not a complete assessment. The goal is to understand the incident well enough to contain it, address the cause, make informed notification decisions, and recover without reintroducing the threat. The FTC describes independent forensic investigators as able to determine a breach’s source and scope, capture and analyze evidence, and outline remediation.
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- Systems and accounts: Which endpoints, servers, cloud services, business accounts, and network devices were affected or could have been reached?
- Entry route and timeline: What evidence indicates how access began, when it occurred, and what the attacker did? The timeline should distinguish supported findings from unknowns.
- Ongoing access: Is there evidence of an active intruder, persistence, or other access that must be removed before recovery?
- Data exposure: What personal, financial, customer, employee, or business information may have been accessed or removed? What evidence supports that conclusion, and what remains uncertain?
- Control failures and remediation: Which vulnerability or security control needs attention, and what containment, eradication, and recovery measures are required?
These are practical assessment goals drawn from CISA’s guidance to identify affected systems and review detection systems and logs, and FTC guidance to establish the source and scope and verify what information was compromised. A responder should explain the evidence behind findings and clearly identify unresolved questions.
Who to involve and how to choose a responder
Build a response team around the incident
The FTC recommends mobilizing a breach-response team that may include forensics, legal, information security, IT, operations, human resources, communications, and management, depending on the organization and incident. A small business may assign several roles to the same people, but technical findings, business decisions, and legal advice should still be clearly owned.
Consider an independent forensic investigator for evidence collection and analysis, and consult legal counsel—potentially outside counsel with privacy and data-security expertise. CISA says organizations should strongly consider help from a reputable third-party incident-response provider in a data breach. These are service categories, not endorsements of particular providers.
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Ask about scope and deliverables before work begins
When comparing providers, focus on whether they can preserve and analyze evidence, have relevant incident experience, work independently, and coordinate with counsel and business operations. Ask for a written scope that explains what systems and evidence they will examine, what deliverables they will provide, how they will communicate findings, and what decisions remain yours or your counsel’s. These are practical selection criteria based on the duties described in federal guidance; the cited sources do not establish any provider’s price, quality, or availability.
How responders determine what happened
Evidence can be lost through routine log rotation, device changes, or shutdown. Ask responders promptly which evidence sources matter and how they should be preserved. CISA specifically identifies system memory, Windows Security logs, and firewall log buffers as potentially volatile or limited-retention evidence. Logs from endpoints, network devices, and cloud services may also help establish the sequence of activity, subject to what each service retained.
Do not make an unsupported conclusion about data theft simply because a system was compromised—or rule it out because no obvious files are missing. The assessment should connect conclusions about access and possible exfiltration to available evidence, state material gaps, and explain what further review could resolve them. The FTC advises using forensic investigators to capture and analyze evidence and to verify the information compromised.
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How to handle notification and communications
Notification is a legal and factual decision, not a single universal deadline or template. In the United States, FTC guidance says every state, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands has a law requiring notification for security breaches involving personal information. Requirements differ, and other obligations may apply based on the data, sector, contracts, affected parties, jurisdiction, and incident facts. Ask counsel to assess the applicable rules and deadlines.
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Coordinate notification timing and content with counsel, relevant regulators, and law enforcement where appropriate, so that communications do not impede an investigation. Reporting an incident to authorities does not replace legal notification duties. CISA’s guide identifies CISA, a local FBI field office, the FBI Internet Crime Complaint Center, and the U.S. Secret Service as possible reporting routes for ransomware incidents; the appropriate route depends on the event. The FTC also discusses local law enforcement and, where appropriate, FBI or Secret Service offices.
Assign a communications point person and prepare clear, accurate answers for affected audiences. Explain what is known, what people should do to protect themselves, and how updates will be provided. Avoid speculation, misleading assurances, and disclosures that could put people at further risk.
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What to do before restoring systems
Agree with the response team on containment and remediation before bringing systems back into service. CISA recommends restoring from offline, encrypted backups according to business priorities and ensuring compromised systems are not reintroduced into a clean recovery environment. A backup is useful only if it is trustworthy and the restored environment does not recreate the same access or vulnerability. Follow the response team’s recovery plan rather than reconnecting systems as soon as they appear usable.
After recovery, document lessons learned and update relevant policies, plans, and procedures. The FTC likewise advises fixing vulnerabilities and implementing recommended remediation. NIST’s current incident-response publication is SP 800-61 Revision 3, which superseded Revision 2; NIST announced the revision in April 2025 in its update notice.
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