What Is SIEM? Security Information and Event Management for SMEs

What Is a SIEM and How Does It Work?

Security Information and Event Management (SIEM) is a category of security technology that combines two functions: security information management (collecting and storing security logs) and security event management (analysing logs in real time to detect threats). A SIEM platform ingests log data from across the IT environment — Windows event logs from endpoints and servers, authentication logs from Active Directory or Entra ID, firewall and network device logs, cloud service audit logs, and security tool alerts — and analyses this data continuously.

The detection power of SIEM comes from correlation. A single failed login attempt is not an alert worth investigating. But a pattern of failed logins from multiple geographic locations, followed by a successful login from an unfamiliar location, followed by bulk email forwarding being configured — each individual event is explainable; together they indicate a compromised account. SIEM's correlation engine identifies these patterns across sources and time, generating a single actionable alert.

Why SIEM Is Challenging for SMEs

Traditional SIEM platforms — Microsoft Sentinel, Splunk, IBM QRadar — are powerful but complex. Configuring detection rules, tuning to reduce false positives (where legitimate activity triggers alerts), maintaining the log ingestion pipelines, and then investigating every alert requires dedicated security expertise. Security Operations Centre (SOC) teams at large organisations typically spend significant time just managing their SIEM.

For most UK SMEs without dedicated security staff, operating a SIEM in-house is not practical. A SIEM that generates hundreds of daily alerts that no one investigates provides no security benefit. This is not a theoretical concern — it is the reality for many organisations that have deployed SIEM tools without the analyst capacity to use them effectively.

SIEM for Microsoft 365 Environments

For businesses using Microsoft 365, Microsoft provides built-in security monitoring through the Microsoft 365 Defender portal. Microsoft Sentinel, Microsoft's cloud-native SIEM, ingests M365 Defender alerts, Azure Active Directory (Entra ID) sign-in logs, and other Microsoft telemetry into a centralised analysis platform. This provides the correlation and log retention capabilities of SIEM within the Microsoft ecosystem.

AMVIA uses Microsoft Sentinel as the SIEM layer for MDR clients requiring full log correlation capability. For most SME clients, AMVIA's MDR service provides equivalent detection by combining Microsoft 365 Defender's built-in correlation with AMVIA's AmviaIQ monitoring platform and human analyst investigation — without requiring clients to manage a full Sentinel deployment independently.

MDR vs SIEM: What SMEs Actually Need

The distinction between SIEM (a technology) and MDR (a service) is important for SME security planning. A SIEM tool generates alerts — humans must investigate and respond. An MDR service includes the human analysts who do the investigating and responding, using SIEM technology as the underlying platform. For SMEs, the bottleneck is not having a place to collect logs — it is having the expertise to turn log data into security outcomes.

Most UK SMEs need MDR, not a standalone SIEM. AMVIA's MDR service provides cross-source threat detection, alert investigation, and active response — the outcomes that SIEM enables, delivered as a managed service rather than a technology the client must operate themselves.

Key Considerations for UK SMEs

• SIEM is a technology platform — it requires people to configure, maintain, and investigate its output to provide value
• For businesses without dedicated security staff, MDR delivers SIEM-equivalent detection outcomes as a managed service
• Log retention requirements may be driven by compliance — some regulations require audit trail retention for specified periods
• Microsoft 365 Defender provides built-in cross-service correlation for M365 environments — a good starting point before considering dedicated SIEM
• Assess detection maturity first — the question is not "do we have a SIEM?" but "are suspicious events being detected and investigated?"

How AMVIA Can Help

AMVIA provides managed detection and response as a service that delivers SIEM-equivalent visibility for UK SMEs. AMVIA's AmviaIQ platform aggregates security signals from Microsoft 365 Defender, endpoint security tools, and network monitoring — correlating events and escalating genuine threats for investigation. For clients requiring full SIEM log retention and correlation capability, AMVIA can deploy and manage Microsoft Sentinel. Contact AMVIA on 0333 733 8050 to discuss security monitoring requirements for your business.