An insider threat is risk originating from someone with authorised access — an employee, contractor or partner. It is difficult to detect precisely because the activity uses legitimate credentials and often looks like normal work, so the evidence is usually a deviation from a person's own baseline rather than an obvious intrusion.
Three categories, requiring different responses
Malicious. Deliberate theft, sabotage or fraud. The smallest category and the one that generates litigation.
Negligent. Someone who bypasses a control to get work done, emails a document to a personal account for convenience, or misconfigures a system. Far more common, and responsible for a large share of actual data loss.
Compromised. An outsider using an insider's credentials. Technically an external attack, but every indicator looks internal — which is why the distinction matters at the start of an investigation, and why assuming malice before checking for compromise has produced some badly wrong conclusions.
An investigation that begins by asking which of the three it is tends to go better than one that begins with a suspect.
Why detection is hard
External intrusion produces signals that are anomalous by definition: unfamiliar addresses, exploitation attempts, unusual protocols. An insider produces none of that. They log in normally, from the usual place, and open files they are entitled to open.
What remains is behavioural. Access volume departing from the person's own history, activity at unusual hours, interest in material outside their role, or a sudden pattern of bulk downloads. All of that requires a baseline, which requires logging that was configured before anyone needed it — and this is where most organisations find themselves short.
The artifacts that matter
When an investigation does begin, the productive sources are consistent:
- Authentication and access logs, establishing what was reached and when.
- Removable media records — the operating system records device identifiers and connection times.
- Cloud sync clients and personal accounts, particularly ones installed recently.
- Egress records from proxies, firewalls and mail gateways.
- Printing, which is regularly overlooked and regularly decisive.
- HR context — resignation dates, performance history, and access changes.
Investigating people is legally constrained
An internal investigation touching an employee's activity engages employment law, privacy regimes, works-council obligations in some jurisdictions, and potentially union agreements. Monitoring that is lawful in one country is unlawful in another, and a multinational investigation run on a single set of assumptions is a recognised way to convert a data-loss problem into an employment claim.
Counsel should be involved before the monitoring starts, not after the findings are in.
Where the balance actually sits
Aggressive monitoring damages the trust that makes an organisation work, and most insider incidents are negligent rather than malicious. The controls that reduce risk without corroding culture are mostly structural rather than surveillance-based: least-privilege access, prompt removal of access at offboarding, separation of duties on financially sensitive processes, and alerting on the narrow set of behaviours that are genuinely anomalous — bulk export, mass deletion, access to material well outside a role.
The departure window deserves specific attention, because that is when a disproportionate share of incidents occur and when preservation is most often defeated by routine IT process.
From our work
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