Hackers don’t break in, they log in

A new study has found that the primary way attackers gained initial access to networks was by exploiting external remote services, which include edge devices such as firewalls and VPNs, and by leveraging valid accounts.

The 2025 Sophos Active Adversary Report details attacker behaviour and techniques from over 400 Managed Detection and Response (MDR) and Incident Response (IR) cases in 2024.

The combination of external remote services and valid accounts aligns with the top root causes of attacks. For the second year in row, compromised credentials were the number one root cause of attacks (41% of cases). This was followed by exploited vulnerabilities (21.79%) and brute force attacks (21.07%).

Understanding The Speed of Attacks

When analysing MDR and IR investigations, the Sophos X-Ops team looked specifically at ransomware, data exfiltration, and data extortion cases to identify how fast attackers progressed through the stages of an attack within an organisation. In those three types of cases, the median time between the start of an attack and exfiltration was only 72.98 hours (3.04 days). Furthermore, there was only a median of 2.7 hours from exfiltration to attack detection.

“Passive security is no longer enough,” said John Shier, field CISO at Sophos. “While prevention is essential, rapid response is critical. Organisations must actively monitor networks and act swiftly against observed telemetry. 

“Coordinated attacks by motivated adversaries require a coordinated defence. For many organisations, that means combining business-specific knowledge with expert-led detection and response. Our report confirms that organisations with proactive monitoring detect attacks faster and experience better outcomes.”

Other Key Findings from the 2025 Sophos Active Adversary Report:

• Attackers Can Take Control of a System in Just 11 Hours: The median time between attackers’ initial action and their first (often successful) attempt to breach Active Directory (AD) – arguably one of the most important assets in any Windows network – was just 11 hours. If successful, attackers can more easily take control of the organisation.
• Top Ransomware Groups in Sophos Cases: Akira was the most frequently encountered ransomware group in 2024, followed by Fog and LockBit (despite a multi-government takedown of LockBit earlier in the year).
• Dwell Time is Down to Just 2 Days: Overall, dwell time – the time from the start of an attack to when it is detected – decreased from 4 days to just 2 in 2024, largely due to the addition of MDR cases to the dataset.
• Dwell Time in IR Cases: Dwell time remained stable at 4 days for ransomware attacks and 11.5 days for non-ransomware cases.
• Dwell Time in MDR Cases: In MDR investigations, dwell time was only 3 days for ransomware cases and just 1 day for non-ransomware cases, suggesting MDR teams are able to more quickly detect and respond to attacks.
• Ransomware Groups Work Overnight: In 2024, 83% of ransomware binaries were dropped outside of the targets’ local business hours.
• Remote Desktop Protocol Continues to Dominate: RDP was involved in 84% of MDR/IR cases, making it the most frequently abused Microsoft tool.

To shore up their defences, Sophos recommends that companies do the following:

• Close exposed RDP ports
• Use phishing-resistant multifactor authentication (MFA) wherever possible
• Patch vulnerable systems in a timely manner, with a particular focus on internet-facing devices and services
• Deploy EDR or MDR and ensure it is proactively monitored 24/7
• Establish a comprehensive incident response plan and test it regularly through simulations or tabletop exercises

Read the full It Takes Two: The 2025 Sophos Active Adversary Report on Sophos.com.