Threat Focus: Insider Threat – Guarding Against Human Fallibility

In cyber security, attention often centres on external adversaries, ransomware gangs, nation-state actors, and sophisticated phishing campaigns. Yet for many UK organisations, the most immediate and underestimated risk originates within the network itself: the insider. The NCSC Annual Review 2025 reinforces that human error remains the leading cause of UK cyber incidents, accounting for the majority of reported breaches. Whether through a misdirected email, a misconfigured cloud service, or a stolen password, the everyday actions of employees often create the openings that attackers exploit.

This insider risk takes three distinct forms: the negligent insider, the malicious insider, and the compromised insider. The Synnovis ransomware attack in June 2024, which disrupted NHS pathology services, illustrated the last category vividly. Although executed by the Qilin ransomware group, it was the compromise of valid employee credentials that opened the door, turning a minor lapse into a systemic outage. As the NCSC notes, adversaries increasingly leverage legitimate accounts to evade detection, making identity the new battleground.

Mitigating insider threats requires an integrated strategy combining technical enforcement and behavioural resilience. Access control remains foundational: Multi-Factor Authentication (MFA) blocks over 99% of credential-based attacks, according to CrowdStrike’s 2025 Global Threat Report, while applying least privilege limits the potential damage from any single user. Complementary monitoring, such as User and Entity Behaviour Analytics (UEBA), enhances visibility, flagging anomalous access or data movement that may signal misuse or compromise.

However, technology alone cannot solve human fallibility. Training remains essential, yet its long-term impact is limited. Recently published research from the University of Chicago found that phishing-awareness improvements fade within weeks without reinforcement. KnowBe4’s 2025 Phishing by Industry Benchmark Report echoes this, showing that ongoing, bite-sized simulations are the only proven way to maintain vigilance. Pairing these programs with modern endpoint resilience tools, such as targeted anti-ransomware tools, ensures that even when human error occurs, containment and recovery are rapid.

Beyond controls and training, leaders must also consider the human motivations that drive behaviour. Disgruntled or disengaged employees are far more likely to rationalise data theft or accept external bribes, especially if they feel undervalued or financially strained. Recognition for good security hygiene, transparent communication about company goals, and visible pathways for career growth all strengthen psychological ownership. When staff feel trusted, fairly treated, and part of a shared mission, the likelihood of malicious intent drops sharply. Happy, motivated employees are key to the defence against insider threats.

Ultimately, insider threats reflect the intersection of people, process, and technology. As the NCSC highlights, building defences around human behaviour, not just against it, is now the defining measure of a mature cyber security strategy.