Stopping a Phishing Attack in Its Tracks with Microsoft Sentinel
How a payroll company detected and contained a phishing attack within one hour using Microsoft Sentinel — maintaining client trust and regulatory compliance.
Industry
Payroll & Workforce Management
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:
Because of the rapid response and comprehensive visibility provided by Sentinel, no sensitive data was accessed or exfiltrated.
The attacker's session was terminated
Login tokens were revoked
The user's password was reset
An investigation was launched
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
The Challenges
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.
The Solution
We deployed Microsoft Sentinel as the company's cloud-native SIEM. Over just a few days, we integrated key log sources including:
The company's internal IT team took responsibility for ongoing monitoring, with an on-call technician receiving PagerDuty alerts for high-priority incidents.
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 Results
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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