Handling insider threat incidents: malicious, negligent and compromised insiders
In short: An insider threat comes from someone with legitimate access, such as an employee, contractor or partner, who causes harm deliberately, by mistake or because their account was taken over. Insider incidents must be handled discreetly, with HR and legal involved from the start, proportionate monitoring, careful evidence handling and coordinated removal of access.
What makes insider incidents different
Most incident response assumes an outside attacker. With an insider threat, the person involved already has legitimate access, knows your systems and may be someone colleagues trust. That changes how you investigate. You must protect evidence and the organisation, but also treat the person fairly, respect privacy law and avoid accusing anyone before the facts are clear. Many insider incidents turn out to be honest mistakes.
Three types of insider
| Type | Example | Response focus |
|---|---|---|
| Malicious | A departing salesperson copies the customer list to a personal cloud drive | Evidence, legal options, recovering the data |
| Negligent | A staff member emails a spreadsheet of personal data to the wrong person | Containment, breach assessment, training |
| Compromised | An attacker uses a phished employee account | Treat as an external attack; support the employee |
Possible warning signs include unusual access to data outside someone's role, large downloads or uploads, activity at odd hours, attempts to bypass controls and, for leavers, sudden bulk copying in their final weeks. None of these proves wrongdoing alone; they are reasons to look more closely.
Running the response
- Keep it need-to-know: form a small group with security, HR, legal and data protection. Avoid alerting the person or spreading rumours.
- Check authority and policy: make sure monitoring is covered by your acceptable use and monitoring policies and is proportionate under data protection law.
- Preserve evidence: collect logs, email and device data in a forensically sound way, with a chain of custody, in case of disciplinary or legal action.
- Contain in coordination with HR: disabling an account, collecting a laptop and holding a meeting should happen together, so data cannot be destroyed or moved in between.
- Assess impact: what data was accessed or taken? Does it involve personal data that must be reported to the regulator?
- Close and learn: record the outcome and fix the gaps that allowed it.
Tip: the security team gathers facts; HR and management make employment decisions. Keeping those roles separate protects both the organisation and the individual.
Reducing insider risk
- Least privilege: people get only the access their role needs, reviewed regularly.
- Joiners, movers and leavers process: remove access on the last day, and adjust it when people change role.
- Data loss prevention and alerts for bulk downloads or uploads to personal storage.
- User and entity behaviour analytics (UEBA), which flags activity unusual for that person.
- A healthy culture: clear policies, training and a safe way to report mistakes quickly. People who fear blame hide errors.
Real-world example: a leaver at a recruitment agency
At a fictional recruitment agency, a DLP alert shows that a consultant who has resigned uploaded 4,000 candidate records to a personal file-sharing account. The security lead informs HR and the data protection officer only. They confirm the upload in the cloud audit logs and preserve the evidence. That afternoon HR meets the consultant while IT disables the account at the same time and collects the laptop. With legal advice, the agency asks for the data to be deleted and confirmed in writing, assesses the risk to candidates and reports the breach to the Information Commissioner's Office within 72 hours. It then blocks uploads to personal cloud storage from company devices.
Practice
What are the three types of insider threat?
Why should disabling access be coordinated with HR?
Name two controls that reduce insider risk.
Key takeaways
- Insiders already have legitimate access, so response must be discreet and fair.
- Insiders can be malicious, negligent or compromised.
- Involve HR, legal and data protection from the start.
- Preserve evidence and coordinate access removal with HR.
- Least privilege, leaver processes and DLP reduce insider risk.
Original content written by Mohamed Fayas for FM TecHub. © 2026 FM TecHub. You're welcome to share a link to this page; please don't copy the text elsewhere without permission.