What Is SIEM and Do I Need It?

Quick answer: SIEM (Security Information and Event Management) collects logs from across your environment, correlates events, and detects threats. It's powerful for threat detection and compliance but expensive and complex. Most SMEs don't need full SIEM—lighter alternatives like MDR often make more sense.

What SIEM Does

Log collection

Gathers data from everywhere:

• Firewalls and network devices
• Servers and endpoints
• Cloud services (M365, Azure, AWS)
• Applications
• Identity systems
• Security tools

All security-relevant events in one place.

Correlation and analysis

Connects the dots:

• User logged in from unusual location
• Same user accessed sensitive file share
• Same user sent large email attachment externally

Individual events might be normal. Together? Suspicious. SIEM finds patterns.

Alerting

Notifies when something's wrong:

• Real-time alerts on detected threats
• Prioritised by severity
• Contextual information for investigation

Investigation and forensics

Enables deep analysis:

• Historical data for investigation
• Timeline reconstruction
• Evidence preservation
• Root cause analysis

Compliance reporting

Proves you're monitoring:

• Log retention
• Audit trails
• Compliance reports
• Evidence for auditors

The Reality of SIEM

The good

• Comprehensive visibility
• Advanced threat detection
• Compliance requirement satisfaction
• Incident investigation capability
• Correlation across sources

The challenging

Cost:

• Software licensing (expensive)
• Storage (logs are big)
• Infrastructure
• Personnel (needs analysts)

Complexity:

• Deployment takes months
• Ongoing tuning required
• False positive management
• Skills required to operate

Alert fatigue:

• SIEMs generate lots of alerts
• Most are false positives or noise
• Without analysts, alerts are ignored
• A SIEM nobody watches is useless

Do You Need SIEM?

Yes, if:

• Compliance requires it (CAF, NIS2, some ISO 27001 interpretations)
• Regulatory expectations (financial services, critical infrastructure)
• Large, complex environment (many systems, significant data)
• In-house security team to operate it
• Significant budget for implementation and ongoing

Probably not, if:

• Under 100 employees (usually)
• No compliance requirement for log monitoring
• No security team to watch alerts
• Limited budget (better spent elsewhere)
• Simple environment (mostly cloud/SaaS)

Alternatives to Full SIEM

MDR (Managed Detection and Response)

What it is: EDR + 24/7 human monitoring and response

Advantages:

• Lower cost than SIEM
• Includes human analysts
• Faster deployment
• Managed service (their problem)

Limitations:

• Focused on endpoints (not everything)
• Less customisation
• Dependent on provider

For most SMEs, MDR is better value than SIEM.

Microsoft Sentinel (Cloud SIEM)

What it is: Cloud-native SIEM as a service

Advantages:

• No infrastructure to manage
• Deep M365/Azure integration
• Pay-per-use pricing
• Modern, scalable

Limitations:

• Still needs tuning and management
• Can get expensive with high volumes
• Still needs analysts (or managed service)

Security-focused MSP/MSSP

What it is: Us managing security monitoring for you

Advantages:

• Expertise included
• Right-sized for your organisation
• Single provider accountability
• Compliance evidence provided

Questions to Ask

Before buying SIEM:

1. What compliance requirement demands it?
2. Who will monitor the alerts?
3. What's the total cost (software + infrastructure + people)?
4. Would MDR meet the same need for less?
5. Is our environment complex enough to justify it?

Be honest: Most organisations buying SIEM can't operate it effectively.

Our Approach

We provide appropriate monitoring for each client:

For most clients:

• MDR for endpoint detection
• M365 security alerting
• Firewall log review
• Managed by our team

For clients requiring SIEM:

• Microsoft Sentinel deployment
• UK-based SIEM (Assuria) for specific requirements
• Managed service option
• Compliance reporting

We help you choose what's right—not what generates the biggest invoice.

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about the right approach for your organisation.

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