Cyber security threats in 2025 have become more advanced, with attackers leveraging AI, supply chain vulnerabilities, and geo-political tensions to launch increasingly sophisticated and targeted campaigns.
As cyber threats grow in complexity and capability, Defence in Depth remains one of the most effective strategies to protect organisations against threats and mitigate the advancement of cyber attacks.
What is Defence in Depth?
Defence in Depth is a layered security approach that ensures multiple safeguards are in place to protect against various attack vectors.
Rather than relying on a single security measure, this strategy integrates multiple defensive layers. These defensive layers range from physical and network security to user training and incident response. The benefit of this layered approach to defence is that if one layer is breached, others continue to provide protection.
The 2025 Cyber Threat Landscape
According to the NCSC Cyber Security Breaches Survey 2024, 50% of businesses reported experiencing a cyber-attack or breach in the past year. While larger enterprises remain primary targets, 32% of medium-sized businesses and 27% of small businesses also faced cyber incidents, highlighting the growing need for strong cyber security strategies. [source: NCSC]
Increased Attacks on Critical National Infrastructure & Supply Chains
Nation-state actors and cyber-criminal groups are increasingly targeting essential services such as energy, water, healthcare, and transportation. Supply chain attacks have also surged, with attackers infiltrating widely used software and IT providers to gain access to multiple organisations at once.
Defence in Depth Mitigation:
• Network segmentation to isolate critical assets.
• Continuous monitoring and risk assessment of third-party vendors.
• Zero Trust architecture to limit access to essential systems.
• Incident response planning for handling supply chain disruptions.
Rise in Ransomware & Data Extortion Attacks
Ransomware remains a top threat, with attackers adopting double and triple extortion tactics. The 2024 survey found that 19% of businesses that suffered a breach were targeted by ransomware, often leading to financial and reputational damage.
Defence in Depth Mitigation:
• Regular vulnerability scanning and patch management.
• Penetration testing across the IT estate
• Immutable backups to protect against data loss.
• Network segmentation to limit ransomware spread.
AI-Driven Social Engineering & Business Email Compromise (BEC)
Cybercriminals have now started using AI-powered phishing campaigns, deepfake technology, and social engineering tactics to manipulate employees and executives into revealing sensitive information or transferring funds.
According to the UK Department for Science, Innovation & Technology phishing remains the most common type of cyber incident in 2025, with 74% of businesses and 72% of charities reporting they experienced a phishing incident in the past 12 months.
Defence in Depth Mitigation:
• Email filtering and anomaly detection. Consider AI-powered tools that can intuitively detect and remove even the most a9odvanced phishing emails.
• Multi-factor/2-factor authentication (MFA/2FA) remains the single most effective control against phishing attempts.
• Security awareness training focused on AI-driven threats.
• Verification processes for high-value transactions.
Implementing Defence in Depth: A Multi-Layered Approach
Defence in Depth was originally adapted from an ancient military strategy, designed to slow the advancement of an attacking enemy so that they exhaust their resources and lose momentum.
Translated into the field of cyber security, this strategy can buy targeted organisations vital time to adapt and respond to the incident, ensuring the most sensitive assets remain protected.
To be prepared to face a real cyber incident, organisations must implement a Defence in Depth strategy that covers all aspects of cyber security, including:
1. Physical Security – Secure data centres, restrict access, and implement biometric authentication. Physical penetration testing such as Red Team/Tiger Team exercises should be conducted on physical security measures, assessing access control weaknesses, surveillance blind spots, and the effectiveness of security response procedures. Red Team exercises can simulate real-world intrusions, testing how well physical security controls prevent unauthorised access.
2. Network Security – Deploy firewalls, IDS/IPS, and enforce network segmentation. Regular penetration testing should be conducted against network perimeter defences, external and internal infrastructure, internal network segmentation, and VPN security.
3. Endpoint Security – Use robust endpoint detection & response (EDR) solutions or consider partnering with a managed security services provider (MSSP) for managed detection & response (MDR) services. Testing should evaluate endpoint resilience, including BYOD policies and remote device security.
4. Application Security – Conduct regular security testing and vulnerability assessments of public-facing and internal applications, including any exposed API endpoints.
5. Data Protection – Enforce encryption, access controls, and backup strategies.
6. User Training & Awareness – Conduct ongoing cyber security education to recognise phishing and social engineering threats.
7. Incident Response & Business Continuity – Develop incident response plans, and test them utilising services such as penetration testing and red teaming.
8. Zero Trust Architecture – Use zero-trust architecture and implement strict verification protocols across all access points.
9. Vulnerability Management – Continuously monitor, assess, and remediate security gaps across infrastructure, cloud environments, and operational technology (OT) by using vulnerability management tools, and patching software.
10. Red Teaming & Attack Simulations – Organisations should consider conducting red team assessments, not just against their physical security controls, but to test the overall effectiveness of their Defence in Depth strategy, evaluating how well layers of security work together to detect and respond to advanced persistent threats (APTs) across various sophisticated attack scenarios.
Conclusion: Why Defence in Depth is More Critical Than Ever
As cyber threats become more advanced and widespread, adopting a Defence in Depth approach is no longer optional—it is essential. By implementing multiple layers of security across networks, endpoints, cloud environments, applications, and user domains, organisations can significantly reduce their risk exposure.
Whether securing a nation’s critical infrastructure, a large enterprise, or an SME, a well-planned Defence in Depth strategy ensures resilience against ever-evolving threats.
With AI-powered cyber-attacks, state-sponsored threats, and ransomware innovations reshaping the threat landscape organisations should review their current cyber security strategy today and take pro-active steps to implement a robust Defence in Depth approach.
