An insider threat is a security risk that comes from people inside an organisation – employees, contractors or partners – who misuse their legitimate access, deliberately or by accident.
Types of insider threats
- Malicious insiders steal data, sabotage systems or sell access, for revenge, money or ideology. Ransomware gangs openly recruit employees to plant their malware for a share of the ransom.
- Negligent insiders cause incidents through mistakes: sending files to the wrong person, misconfiguring a cloud storage bucket or falling for social engineering.
- Compromised insiders are legitimate accounts taken over by outside attackers, who then act with the employee’s privileges.
Real cases show the impact: in 2023 Tesla disclosed that two former employees had leaked personal data of more than 75,000 people to a newspaper, and the 2020 Twitter breach started with attackers persuading staff over the phone to hand over access to internal tools.
Why insider threats are hard to detect
Insiders already have valid credentials, know where valuable data is and understand internal processes. Their actions look like normal work, so perimeter defences and signature-based tools rarely notice them.
How to reduce insider risk
- Apply the principle of least privilege and review access rights regularly.
- Use data loss prevention and user behaviour analytics to spot unusual downloads or access.
- Revoke access immediately when people leave or change roles.
- Combine technical monitoring with HR processes, clear policies and security awareness training, and include insider scenarios in threat hunting.
Synonyms:
malicious insider
