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Cyber security discussions often revolve around external attackers. Malware. Phishing. Ransomware gangs. But there is another threat that isn’t trying to break in, it’s already inside. Insider threats in cyber security are complex, human in nature, and often hard to detect using traditional security tools. Insider threats are posed by people with legitimate access to your systems, staff, contractors, suppliers, even former employees. Sometimes the risk comes from honest mistakes. Sometimes it’s intentional. And in today’s hybrid, perimeter-less world, it’s getting harder to tell the difference.
Mimecast’s 2025 survey of over 1,100 IT and security leaders across six countries paints a clear picture: insider risks are growing fast. In the past year, 43% of organisations reported a rise in internal threats or data leaks, most commonly caused by compromised, careless, or negligent employees. Two-thirds of those surveyed (66%) expect insider-driven data loss to increase even further in the year ahead. With the average cost of an insider incident now sitting at around £10.75 million, it’s no longer a risk that can be sideline.
This post explores what insider threats in cyber security really are, why they’re becoming more common, and what businesses can do to manage them without sacrificing trust, productivity or agility.
What Exactly Are Insider Threats in Cyber Security?
An insider threat is any risk to your organisation that stems from someone with authorised access to your network, systems, or data. This access might be legitimate, like a finance team member logging in to process payroll, or residual, such as an ex-employee whose access was never fully revoked.
What makes insider threats so challenging is their invisibility to traditional defences. Firewalls, antivirus software, and intrusion prevention systems are designed to stop unauthorised users. But an insider is already trusted. They’re already inside the wall.
When insiders, knowingly or unknowingly, misuse their access, the impact can be just as damaging as an external breach. Sometimes more so.
Understanding The Different Types of Insider Threats in Cyber Security.
Not all insider threats are malicious. In fact, most aren’t. But whether the motive is carelessness, complacency, or criminal intent, the effect on your organisation can be equally disruptive.
Here’s a more detailed look at the major types of insider threats affecting organisations today.
Negligent Insiders.
By far the most common type of insider threat, negligent insiders are employees or contractors who inadvertently compromise security through everyday mistakes.
This might be someone who falls for a convincing AI generated phishing email, sends a file to the wrong recipient, uploads sensitive documents to an unauthorised cloud app, or reuses weak passwords across different systems. None of it is done with harmful intent, but it creates real openings for attackers to exploit.
The rise in remote and hybrid work has amplified this risk. Employees now work from personal devices, public networks, and home offices, often without the same controls as the corporate environment. And while most are simply trying to get their job done, the line between convenience and risk has become dangerously thin.
Negligent insiders are behind the majority of insider-related incidents. Yet because these behaviours are unintentional, they’re often dismissed until it’s too late.
Compromised Insiders.
A compromised insider is someone whose credentials, device, or account has been hijacked by an external threat actor. On the surface, everything may appear normal, logins from expected locations, use of authorised applications, familiar activity patterns. But behind the scenes, someone else is pulling the strings.
These types of threats are particularly dangerous because they mimic legitimate behaviour. Attackers exploit the trust placed in these users, bypassing detection systems that assume insiders are safe. In many ransomware and supply chain attacks, compromised insiders are the initial entry point.
The challenge here is not just identity theft, it’s identity abuse. Even well-secured accounts can become liabilities once access is granted to the wrong hands.
Malicious Insiders.
These are insiders who act with the explicit intent to cause harm. Their motives may vary, financial gain, resentment, revenge, political ideology, or even coercion by external actors, but their actions are calculated and deliberate.
Malicious insiders might steal intellectual property, leak confidential information, disrupt systems, or manipulate data. In some cases, the attack may be a one-off — a departing employee taking a client list with them. In others, it’s a sustained effort over weeks or months.
Although less common than negligent or compromised users, malicious insiders are typically responsible for the most costly and reputationally damaging breaches. And because they know the systems, processes, and blind spots better than anyone, they can be difficult to catch without active behavioural monitoring.
Opportunistic Insiders.
Sometimes the line between carelessness and intent is blurry. Opportunistic insiders might not set out to do harm, but take advantage when the opportunity presents itself.
This could include someone snooping through HR files they shouldn’t access, copying confidential designs to use in a future role, or exploiting the fact that their access was never revoked after a departmental change. Their mindset is often: “If the system lets me do it, it must be okay.”
The problem is that these types of incidents often fall outside formal policy violations. They’re not always criminal. But they reflect weak internal controls and can lead to serious regulatory and reputational consequences.
Manipulated Insiders.
Attackers trick or socially engineer users into acting against their organisation’s best interests. The security community often calls these individuals “pawns” because attackers deceive them through impersonation, pressure, or emotional manipulation.
A threat actor might send a convincing email to a junior employee, posing as the CEO and urgently requesting access to a secure document. Or they might convince a support team member to reset a password by pretending to be someone locked out of a critical system.
These insiders aren’t acting out of malice, but the result is the same. Their access is misused, and sensitive data is exposed.
In a world of increasingly sophisticated social engineering, these scenarios are no longer rare. They’re routine.
Why insider threats are on the rise
Several changes in the way we work and manage technology have made insider threats more difficult to control.
Hybrid work has blurred the boundary between personal and corporate environments. Cloud services have introduced more flexibility, but also more access points. Third-party vendors are increasingly embedded into core operations, sometimes with extensive system privileges. And traditional network perimeters have all but disappeared.
Meanwhile, identity sprawl is growing. Employees use dozens of applications, each with its own login. The more accounts and credentials in circulation, the greater the chance of compromise, especially when password hygiene is poor or access is never reviewed.
These changes have turned identity into the new perimeter. And insider threats into one of the most urgent cyber security risks facing modern organisations.
A Smarter Approach to Managing Insider Threats.
You can’t eliminate risk entirely. But you can reduce your exposure, and respond faster when something doesn’t feel right.
The most effective insider threat strategies don’t rely on a single tool. They combine technology, process, and culture.
Start by limiting access. No one should have more access than they need. Review permissions regularly, and make sure access changes immediately when someone changes roles or leaves the business.
Move toward a Zero Trust model. That means verifying every user and device before granting access, no matter where they’re located. Trust is never assumed, it’s earned continuously, based on identity, device health, behaviour, and risk context.
Monitor behaviour, not just logins. Unusual file movement, login patterns, or privilege escalations can often indicate a compromised or malicious user, long before damage is done.
And above all, focus on people. Train your teams. Show them how attacks happen. Make it easy to report suspicious activity. Build a culture where security isn’t just a compliance requirement, it’s part of how you operate.
Always on. Always aware.
At Secon, we believe cyber security should work with people, not against them. We help our clients simplify complexity, reduce risk, and build defences that don’t just keep attackers out, but protect against threats that already live within the business.
Insider threats aren’t just a technology issue. They’re about identity. Access. Behaviour. And trust.
We’re here to help you manage all four. Get in touch to discover how we can support in making your organisation more secure, inside out.