Microsoft Defender for Business vs Third-Party MDR: Which Is Best for SMEs?

This is the core of the defender vs mdr decision: you are not choosing between two competing products. You are deciding whether the security tooling already inside your Microsoft 365 security licence runs unwatched, or whether trained analysts respond to what it finds. The tool is the easy part. The watching is where SMEs get caught out.

What is the difference between Defender and MDR?

Defender for Business is endpoint detection and response (EDR) software included in Microsoft 365 Business Premium. MDR is a managed service: a security operations centre (SOC) of analysts who use an EDR engine like Defender to monitor your estate around the clock, triage every alert, and contain attacks on your behalf.

Put simply, Defender produces alerts; MDR turns those alerts into action. A modern EDR platform such as Microsoft Defender for Business will flag credential theft, suspicious sign-ins and malware — but flagging is not stopping. Managed detection and response (MDR) adds the human judgement and out-of-hours cover that decides whether an alert at 02:00 on a Sunday becomes a contained incident or a Monday-morning ransomware headline.

Defender vs MDR: side-by-side comparison

The two are layers in the same stack, not rivals. Defender is the sensor; MDR is the response team standing over it. The table below shows where each starts and stops, so you can see exactly which gap MDR is paid to close for an SME with no dedicated security staff.

When is Microsoft Defender for Business enough on its own?

Defender alone is defensible only when you have skilled people watching it during the hours attackers operate — which is all of them. If you employ a security analyst who triages alerts daily and can respond out of hours, the tooling in Business Premium may be sufficient without a managed layer on top.

In practice, very few UK SMEs meet that bar. Microsoft's own research found that 99.9% of compromised accounts had not enabled multi-factor authentication (Microsoft, 2019) — a reminder that the gaps are usually in operation, not in the product. Defender will auto-quarantine known malware, but identity-based attacks, lateral movement and "living off the land" techniques generate alerts that need a person to interpret. Left unwatched, that detection capability is a smoke alarm with nobody home.

When does an SME need MDR?

You need MDR the moment detection outpaces your ability to respond — which, for a business without a 24/7 SOC, is immediately. If nobody is rostered to investigate alerts overnight, at weekends and during holidays, the time between detection and response is exactly where attackers do their damage.

The UK threat picture backs this up. The government's Cyber Security Breaches Survey 2025 found 43% of UK businesses experienced a cyber breach or attack in the last year (gov.uk). IBM puts the average time to identify and contain a breach at 241 days (IBM 2025), with an average cost of £8,260 for businesses suffering a negative outcome. Choose MDR when:

• You have no dedicated, in-house security analyst.
• You cannot guarantee a human response to alerts outside office hours.
• You already pay for Business Premium and want the Defender for Business tooling actually monitored.
• You need defensible evidence of 24/7 oversight for clients, insurers or auditors.

How much does MDR cost compared with running Defender alone?

MDR is the cheaper way to get round-the-clock cover than hiring for it. Defender for Business is already included in Microsoft 365 Business Premium at roughly £16.90 per user per month (microsoft.com). Adding MDR layers human monitoring on top for a per-endpoint fee — far less than a salaried analyst.

For any SME under roughly 200 endpoints, MDR is the lower-cost route to continuous coverage. One analyst cannot cover 168 hours a week; a SOC can. The NCSC's guidance on logging and protective monitoring (ncsc.gov.uk) treats continuous oversight as a baseline, not a luxury, which is why 24/7 security monitoring is sold as a service rather than a hire for businesses this size.

What AMVIA recommends

If you have no dedicated in-house security analyst, choose MDR — not Defender standalone. MDR uses Defender (or an equivalent EDR) as the detection layer, then adds 24/7 human monitoring and incident response on top. This maximises the Business Premium investment you already hold rather than bolting on a competing agent.

AMVIA's MDR service starts from £10 per endpoint per month and is built on Microsoft Defender for Endpoint, monitored by AMVIA's in-house 24/7 SOC. It typically replaces both standalone antivirus and the cost of dedicated security staff. That is the whole point of our model: one provider, security-first, Microsoft-certified — so the tool and the team answering for it are never split across two contracts. If you are still weighing the underlying technologies, our MDR vs EDR comparison breaks down the detection layer, and our managed cybersecurity service shows how MDR fits a wider security programme.