Insider Threats
MediumInsider
Also known as: Malicious insider, Negligent insider
Risk from people inside the business, whether malicious, negligent, or compromised.
What it is
An insider threat is a security risk that comes from within your organisation: current or former employees, contractors or partners with legitimate access. It can be malicious (someone deliberately stealing or sabotaging), negligent (an honest mistake such as misdirected email or weak handling of data), or the result of a compromised account being used by an outsider.
How it works
- 1
An insider has legitimate access to systems, data or facilities.
- 2
Malicious insiders misuse that access to steal data, commit fraud, or cause damage, often around resignation or a dispute.
- 3
Negligent insiders cause incidents accidentally, for example emailing sensitive data to the wrong person or mishandling credentials.
- 4
Compromised insiders have their account taken over by an external attacker who then acts as them.
- 5
Because the activity uses valid access, it can look like normal business until harm is done.
Warning signs
- Access to data or systems well beyond what a role requires
- Large or unusual downloads, especially before a departure
- Attempts to bypass security controls or use unauthorised tools
- Sharing of credentials or use of accounts that should be disabled
- Former staff accounts still active after offboarding
Business impact
- Theft or leak of intellectual property and customer data
- Fraud and financial loss
- Sabotage or disruption of systems
- Privacy breaches and the reporting obligations that follow
How to defend against it
Apply least privilege
Give people access only to what their role needs, and review access regularly as roles change.
Offboard promptly and completely
Disable accounts and revoke access the moment someone leaves, following a documented checklist.
Monitor for unusual activity
Alerting on large downloads, off-hours access and privilege changes helps catch misuse early.
Build a positive security culture
Clear policies, training and easy reporting reduce both negligent mistakes and the motivation for malicious acts.
Measure your defences
Use these free Cyber Toolkit tools to check how exposed you are and close the gaps this threat exploits.
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