Stopping a Business Email Compromise Attack

When Business Email Compromise Hit a Growing Company, How We Shut It Down and Strengthened Their Defenses

Business Email Compromise (BEC) remains one of the fastest-growing cyber threats facing organizations in 2025 and 2026. Unlike ransomware attacks that often create immediate disruption, BEC attacks are designed to operate quietly. Attackers focus on manipulating trusted communications, stealing credentials, and redirecting financial transactions without triggering traditional security alerts.

At Epis Technology, we recently worked with a growing company that became the target of a sophisticated business email compromise attack. What started as a seemingly legitimate vendor communication quickly escalated into a serious security incident involving compromised credentials, unauthorized mailbox access, and attempted financial fraud.

Fortunately, the issue was identified before any funds were transferred, allowing our team to contain the threat and strengthen the organization’s defenses before further damage occurred.

The Attack Looked Completely Legitimate

The company regularly worked with vendors, suppliers, and service providers through email. Employees exchanged invoices, payment instructions, contracts, and project updates every day.

The finance department received an email that appeared to come from a trusted business partner requesting updated payment information for an upcoming transaction.

The message looked authentic because:

• The sender appeared legitimate
• The email thread contained previous conversations
• The wording matched normal communication patterns
• The request aligned with an active project

At first glance, there was no obvious reason to suspect fraud.

How the Attackers Gained Access

Our investigation revealed that attackers had compromised an external email account and spent time monitoring communications before taking action.

This type of attack has become increasingly common because cybercriminals now prioritize patience and precision over mass phishing campaigns.

The attackers had:

• Monitored vendor communications
• Studied payment approval processes
• Identified key employees
• Waited for a high-value transaction opportunity

Instead of sending malware, they simply inserted themselves into a trusted business conversation.

The Warning Sign That Prevented a Loss

Fortunately, a member of the finance team noticed a small inconsistency in the payment instructions and escalated the request for verification.

That single decision prevented a potentially significant financial loss.

The company contacted Epis Technology to perform an immediate security assessment.

What We Discovered

Our investigation identified several concerning issues:

• Unauthorized mailbox access
• Suspicious login activity
• Malicious forwarding rules
• Incomplete multi-factor authentication coverage
• Limited mailbox monitoring
• Weak conditional access policies

While only one account showed signs of compromise, the environment contained several weaknesses that could have enabled future attacks.

Immediate Containment Actions

Once the compromise was confirmed, Epis Technology launched a rapid response process.

We immediately:

• Revoked active sessions
• Reset compromised credentials
• Removed malicious mailbox rules
• Reviewed sign-in logs
• Audited permissions
• Blocked suspicious access attempts
• Verified mailbox integrity

These actions stopped the attack before it could spread further through the organization.

Strengthening Microsoft 365 Security

The incident highlighted the need for stronger identity and email protection.

Over the following days, we implemented several improvements.

Multi-Factor Authentication Expansion

MFA was enforced across all users, administrative accounts, and privileged access workflows.

Conditional Access Policies

We configured risk-based access controls to restrict unauthorized login attempts and improve visibility into suspicious behavior.

Enhanced Anti-Phishing Protection

Microsoft 365 security policies were strengthened to improve:

• Impersonation detection
• Link protection
• Attachment filtering
• Domain reputation monitoring

Administrative Security Reviews

Privileged accounts were reviewed and hardened to reduce exposure to future attacks.

Why Backup Protection Matters During Email Attacks

Many organizations focus on preventing compromise but overlook recovery readiness.

If attackers gain access to a mailbox, they may:

• Delete messages
• Remove records
• Modify data
• Purge communication history

As part of the remediation process, Epis Technology implemented additional protection for:

• Exchange Online
• OneDrive
• SharePoint
• Microsoft 365 business data

This ensured the company could recover critical information even if future attacks impacted cloud services.

The Synology Layer of Protection

The organization also relied on Synology infrastructure for storage and backup operations.

We strengthened their environment through:

• Centralized backup management
• Protected document repositories
• Snapshot-enabled recovery
• Backup monitoring
• Disaster recovery planning

Combining Microsoft 365 protection with Synology backup infrastructure created a more resilient business continuity strategy.

What Businesses Are Learning

Business Email Compromise attacks continue to succeed because they target people and processes rather than software vulnerabilities.

Modern organizations need:

• Multi-factor authentication
• Email security controls
• Conditional access policies
• Backup protection
• User awareness training
• Continuous monitoring
• Incident response planning

Even the most advanced security tools can be bypassed if trusted communications are compromised.

About Epis Technology

Epis Technology helps organizations strengthen cybersecurity, protect Microsoft 365 environments, and improve operational resilience through secure infrastructure design and proactive data protection strategies. The company specializes in Synology consulting, Microsoft 365 and Google Workspace backups, large-scale storage solutions, fully managed PC backups, disaster recovery planning, and IT infrastructure optimization.

By combining layered security controls, secure backup architecture, and proactive monitoring, Epis Technology helps businesses reduce risk and maintain operational continuity in an increasingly complex threat landscape.