Case Study: Stopping a Phishing Attack in Its Tracks with Microsoft Sentinel

Industry

Payroll & Workforce Management

Challenge

A payroll services company needed a centralized way to monitor security across a complex environment that included Office 365, firewalls, and servers — all while meeting client-driven compliance requirements. They didn’t have a formal SOC, so they needed a solution their in-house IT team could manage directly.

Solution

We deployed Microsoft Sentinel as the company’s cloud-native SIEM. Over just a few days, we integrated key log sources including:

  • Entra ID (Azure AD) for SSO activity across all critical systems
  • Office 365 for mailbox activity and email threat detection
  • Firewall logs for network activity
  • Windows server logs for endpoint visibility

The company’s internal IT team took responsibility for ongoing monitoring, with an on-call technician receiving PagerDuty alerts for high-priority incidents.

The Incident

Just weeks after deployment, Sentinel detected a suspicious login tied to a user who had unknowingly submitted credentials to a phishing site. The system triggered an immediate alert.

Thanks to Sentinel’s integration with Entra ID, the alert included rich context about the login attempt — including geolocation, device info, and failure patterns. The on-call technician was paged, and within one hour of the initial compromise:

  • The attacker’s session was terminated
  • Login tokens were revoked
  • The user’s password was reset
  • An investigation was launched

Because of the rapid response and comprehensive visibility provided by Sentinel, no sensitive data was accessed or exfiltrated.

Aftermath & Improvements

Following the incident, we led a full security review and identified several opportunities for improvement:

  • Rolled out phishing-resistant MFA to all users
  • Conducted additional security awareness training
  • Tuned Sentinel detections for greater coverage without alert fatigue

Outcome

The SIEM investment paid off immediately. Without a full-time SOC, the company was still able to detect, respond to, and contain a phishing attack before damage was done — maintaining both client trust and regulatory compliance.

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