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What is an insider threat?

An insider threat is the risk that someone who already has legitimate access causes harm. That person may be a staff member, a contractor, or someone similar, and the harm may be on purpose or by mistake. This is not a cue to treat staff as suspects. 12

By Secordit. Last checked: 10 November 2026.

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How it works

  1. Someone already has legitimate access to systems, files or premises. 12
  2. Harm can happen if they take data out on purpose, or misuse privileged access. The NCSC says the majority of insider breaches are not malicious, but are a result of staff performing their daily roles. Illustrations include sending a file to the wrong person, or falling for phishing. 12
  3. NCSC themes are least privilege, logging of privileged activity, and making it harder to copy large amounts of data unnoticed. 12

How it can look

The NCSC has guidance on reducing data being taken out by malicious insiders. It also covers privileged access management as a way to make misuse harder to hide. 12

Warning signs

  • Many people share a powerful admin login, and there is little record of who used it. 21
  • Large amounts of data can be copied or sent out with no review. 1
  • As an illustration, a file can be sent to the wrong person, or a phishing message can trick someone who already has access. The NCSC says most insider breaches are not malicious. 1

What to do now

  1. Give people only the access they need, and protect privileged accounts with strong MFA. 21
  2. Keep a record of privileged activity, and make it harder to copy large amounts of data unnoticed. 12
  3. Treat accidental harm, such as a misdirected file or a successful phishing message, as part of the same risk. See the data breach and phishing pages. 1

UK reporting and support

  • If personal data may have been exposed, see the data breach page and the ICO guidance. This entry is not legal advice. 1
  • For fraud or hacking in England, Wales or Northern Ireland, use Report Fraud. In Scotland, call Police Scotland on 101. 356
  • If money has gone or banking details were shared, call your bank using the number on your card. Or use 159 if your bank participates. 4
  • If someone is in danger, call 999. 56

How to protect yourself

  • Use least privilege, so everyday work does not need a powerful admin login. 21
  • Log privileged activity, and review unusual copying or sending of large amounts of data. 12
  • Help staff spot phishing, because a mistake by someone with access can still cause harm. 1

Frequently asked questions

What is an insider threat, and does it always mean a dishonest employee?

No. An insider threat is the risk that someone who already has legitimate access causes harm. That can be on purpose or by mistake, and the person may be a staff member, a contractor, or someone similar. 12

Should we treat staff as suspects?

No. The useful themes in the NCSC guidance are least privilege, logging of privileged activity, and making it harder to copy large amounts of data unnoticed. 12

Is falling for phishing an insider threat?

The NCSC says the majority of insider breaches are not malicious. Accidental harm is still an insider-related risk. Illustrations include sending a file to the wrong person or falling for phishing. See also the phishing and data breach pages. 1

Matching kit

Joiners, Movers and Leavers Access Checklist · £19 · Digital download.

A printable checklist and editable access record for when people join, change role or leave. It does not replace your own access decisions.

General information, not legal, financial or personalised security advice. Secordit is not a police or bank reporting service.

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Sources

  1. NCSC, Reducing data exfiltration by malicious insiders | National Cyber Security Centre. Accessed 10 November 2026 (Europe/London).
  2. NCSC, Use privileged access management | National Cyber Security Centre. Accessed 10 November 2026 (Europe/London).
  3. Report Fraud, Report Fraud. Accessed 10 November 2026 (Europe/London).
  4. Stop Scams UK, 159 Phone number - Stop Scams UK. Accessed 10 November 2026 (Europe/London).
  5. Police Scotland, How to report a crime - Police Scotland. Accessed 10 November 2026 (Europe/London).
  6. Report Fraud, Reporting cyber crime and fraud or phishing attempts - Report Fraud. Accessed 10 November 2026 (Europe/London).