What to Do After a Phishing Attack or Compromised Business Email Account

A phishing attack can create significant financial, operational and reputational risk for an organization. In many cases, the most serious damage does not occur when an employee clicks a malicious link. Instead, attackers gain access to an email account, monitor communications and wait for an opportunity to commit fraud, steal sensitive information or redirect payments.

If your organization suspects a compromised email account, acting quickly can significantly reduce the impact of the incident.

Report the Incident Immediately

The first priority is reporting the suspected compromise to your IT, security or incident response team.

Even if an employee is unsure whether credentials were entered into a phishing site, immediate notification is critical. Delays give attackers more time to:

• Monitor communications
• Gather sensitive business information
• Launch additional phishing campaigns
• Attempt wire transfer or payment fraud

Early reporting helps security teams investigate the scope of exposure and begin containment activities.

Secure the Affected Account

Once the incident is reported, secure the compromised account as quickly as possible. Below are recommended actions to take.

Change Credentials from a Trusted Device

If the original computer may have been infected with malware, use a trusted device to update credentials. This helps prevent newly created passwords from being captured.

Sign Out of All Active Sessions

Changing a password alone may not remove someone who is already logged in. Force a sign-out from all active sessions to ensure every user must reauthenticate.

Review Multifactor Authentication Settings

Verify that all multifactor authentication (MFA) methods belong to authorized users. Remove unfamiliar authentication apps, phone numbers, or devices.

Remove Unauthorized Access and Persistence Mechanisms

Attackers often establish methods to maintain access even after credentials are changed.

Review the affected account carefully for:

• Suspicious inbox rules
• Unauthorized forwarding addresses
• Hidden message routing rules
• Unknown connected applications
• Unrecognized authentication methods
• Unauthorized mobile devices

Common indicators include rules that automatically delete or hide messages containing terms such as:

• Invoice
• Payment
• Wire transfer
• ACH
• Banking information

These tactics allow attackers to monitor financial conversations and conceal evidence of fraud. Removing these persistence mechanisms is a critical step in preventing continued compromise.

Determine What Was Accessed or Sent

Conduct a thorough review of the account to understand attacker activity.

Review:

• Sent Items
• Deleted Items
• Email forwarding activity
• Login history
• Administrative changes
• External application access

Attackers frequently use compromised accounts to impersonate employees, executives, vendors or business partners.

If suspicious messages were transmitted, notify recipients through a separate communication channel such as a phone call, secure messaging platform or verified contact method.

Do not use the potentially compromised email thread to communicate about the incident.

Assess Financial Risk Immediately

Organizations involved in vendor payments, escrow transactions, financial operations or wire transfers should treat email compromise as a potential financial fraud event.

Review all open transactions and verify:

• Payment instructions
• Banking details
• Vendor communications
• Wire transfer requests
• Change-of-account notifications

Contact counterparties using previously verified phone numbers rather than information contained in email threads.

If Funds Have Already Been Sent

If funds may have been sent to an unauthorized account, contact the financial institution immediately and initiate fraud recovery procedures.

Rapid action can improve the likelihood of fund recovery.

Preserve Evidence for Investigation

Do not delete evidence before security personnel have reviewed it.

Preserve:

• Phishing emails
• Malicious attachments
• Suspicious inbox rules
• Unauthorized forwarding settings
• Fraudulent messages
• Login records

Detailed evidence helps investigators determine:

• How access was obtained
• What information was exposed
• Whether additional users were affected
• Which systems require remediation

Evaluate Business Impact

Following containment, organizations should assess the broader impact of the incident.

Review potential exposure involving:

• Customer data exposure
• Vendor communications
• Confidential business information
• Financial transactions
• Regulatory obligations
• Business continuity risks

Documenting findings helps support compliance efforts, executive communication and future incident response planning.

After your evaluation, implement measures to help reduce future risk.

Enable Multifactor Authentication

MFA remains one of the most effective controls against credential-based attacks.

Strengthen Email Security

Evaluate:

• Email filtering
• Threat detection tools
• Anti-phishing controls
• Domain protection measures

Conduct Employee Security Training

Employees should understand how to:

• Identify phishing attempts
• Verify unusual requests
• Report suspicious activity promptly

Monitor for Ongoing Threats

Attackers frequently target organizations multiple times. Continued monitoring can help identify follow-up attempts before another compromise occurs.

Schedule Regular Security Assessments

Periodic security reviews help identify vulnerabilities before attackers can exploit them.

Strengthen Security Controls

After the immediate threat has been removed, focus on preventing future attacks.

Recommended security measures include:

• Enable multi-factor authentication across all business accounts
• Implement advanced email security protections
• Conduct phishing awareness training
• Monitor for suspicious login activity
• Review privileged account access
• Perform regular security assessments
• Establish and test incident response procedures

Attackers frequently target organizations more than once. Strengthening controls after an incident helps reduce the risk of repeat compromise.

Key Takeaways on Compromised Email Accounts

A compromised email account is more than an IT issue. It can lead to business email compromise, financial fraud, operational disruption and reputational damage.

Organizations that respond quickly, investigate thoroughly and strengthen their security posture are best positioned to reduce losses and prevent future incidents.

If you suspect a phishing attack or email compromise, engage your security team immediately and follow a structured incident response process to contain the threat before it escalates.

Read more Cybersecurity Tips

For more industry and cybersecurity best practices by Stewart CISO, Genady Vishnevetsky, check out the articles below:

• BlobPhish: The Invisible Phishing Threat Bypassing Traditional Security Tools
• That Trusted Google Link Might Be a Phishing Attack
• Deepfake Fraud in Real Estate: What Every Buyer, Seller and Agent Needs to Know

Frequently Asked Questions

How do I know if my email account has been compromised?

Common warning signs include unauthorized login alerts, unexpected password changes, suspicious inbox rules, unfamiliar forwarding addresses, or reports that emails were sent without your knowledge.

What should I do immediately after clicking a phishing link?

Report the incident immediately, stop interacting with the website, change credentials from a trusted device, and notify your IT or security team for investigation.

Is changing my password enough after a phishing attack?

No. Organizations should also revoke active sessions, review multifactor authentication settings, remove unauthorized mailbox rules, and investigate attacker activity.

What is business email compromise (BEC)?

Business email compromise is a form of cybercrime in which attackers use compromised or spoofed email accounts to impersonate trusted individuals and manipulate financial transactions or sensitive communications.

Can a phishing attack lead to wire fraud?

Yes. Attackers frequently monitor compromised inboxes looking for opportunities to alter payment instructions, impersonate vendors, or redirect wire transfers.

What evidence should be preserved after a phishing incident?

Organizations should preserve phishing emails, attachments, screenshots, authentication logs, message traces, security alerts, and suspicious mailbox configurations.

How can businesses reduce phishing risk?

Effective prevention strategies include multifactor authentication, employee awareness training, advanced email security controls, ongoing monitoring, and regular cybersecurity assessments.

When should we engage incident response experts?

Organizations should seek professional support whenever they suspect credential theft, email compromise, financial fraud, ransomware activity, or exposure of sensitive information.