How to Respond When You've Fallen Victim to a Microsoft 365 Phishing Attack Code

If you've clicked on a suspicious link, entered your Microsoft 365 credentials, and provided your MFA code, your account may be compromised. Quick action is essential to minimize damage and prevent further attacks. This guide outlines immediate steps to take when you've fallen victim to a phishing attack targeting your Microsoft 365 account.

Understanding the Threat

When attackers gain access to your Microsoft 365 account, they can:

• Send phishing emails to your contacts using your identity
• Access sensitive information in your emails and files
• Set up mail forwarding rules to collect information
• Use your account to launch attacks against your organization
• Change account recovery options to maintain access

Even if you have MFA enabled (which you absolutely should), sophisticated attacks can bypass this protection through "MFA fatigue" or "prompt bombing" techniques where attackers capture your MFA code in real-time.

Immediate Response Steps

Step 1: Notify IT Security Team

1. Contact IT immediately

• Report the incident to your IT department or security team right away
• Provide details about the phishing message, when you clicked the link, and what information you entered
• Be completely honest—security teams need accurate information to respond effectively

2. If you're an individual or small business without IT support

• Contact Microsoft Support at 1-800-642-7676
• Consider engaging emergency incident response services from a provider like Hexafusion

Step 2: Change Your Password Immediately

1. Change your Microsoft 365 password

• Access https://portal.office.com/account/#security
• Select Password > Change Password
• Create a strong, unique password you haven't used elsewhere

2. Password best practices

• Use at least 12 characters with a mix of upper and lowercase letters, numbers, and symbols
• Avoid common words, personal information, or predictable patterns
• Consider using a password manager to generate and store strong passwords

3. Change passwords for other accounts

• If you use the same or similar passwords elsewhere, change those immediately
• Prioritize financial, email, and other business-critical accounts

Step 3: Reset Your MFA Methods

1. Review and reset your authentication methods

• Go to https://mysignins.microsoft.com/security-info
• Remove and re-add your authentication methods
• If using the Microsoft Authenticator app, re-register the app

2. Check for unfamiliar authentication methods

• Look for any authentication methods you didn't set up
• Pay special attention to phone numbers or email addresses you don't recognize

Step 4: Check for Mail Forwarding Rules and Delegates

1. Check Outlook rules

• Open Outlook on the web at https://outlook.office.com
• Go to Settings > View all Outlook settings
• Select Mail > Rules
• Look for suspicious rules that forward, delete, or move emails
• Delete any rules you didn't create

2. Check mail forwarding settings

• In Outlook settings, go to Mail > Forwarding
• Ensure forwarding is turned off unless you specifically need it

3. Check delegates and shared mailbox access

• Go to Mail > Accounts > Delegate access
• Remove any unfamiliar accounts with access to your mailbox

Step 5: Check for Mobile Device Access

1. Review connected devices

• Go to https://mysignins.microsoft.com/devices
• Look for devices you don't recognize
• Select Revoke for any suspicious devices

2. Check app passwords

• Go to https://mysignins.microsoft.com/security-info
• Look for and remove any app passwords you didn't create

Step 6: Review Recent Sign-in Activity

1. Check sign-in logs

• Visit https://mysignins.microsoft.com/signinattempts
• Look for logins from unfamiliar locations, devices, or at unusual times
• Click Looks unfamiliar? for any suspicious activity

2. Continue monitoring

• Check your sign-in activity regularly for the next few weeks
• Be alert for any unusual activity

Step 7: Notify Contacts

1. Alert your contacts

• Inform colleagues, friends, and business contacts about the compromise
• Warn them not to click on any links or download attachments from recent emails sent by you
• Use an alternative communication method (phone, in-person, or a different email account)

2. Send a clear notification

• Example message: "My email account was recently compromised. Please disregard any unusual emails from me, especially those containing links or attachments. Do not click on any links or provide any information if requested."

Step 8: Scan Your Devices for Malware

1. Run a full system scan

• Use Windows Defender or another trusted antivirus solution
• Perform a full system scan on all devices used to access your email

2. Consider advanced endpoint detection tools

• For businesses, consider deploying Microsoft Defender for Endpoint or similar EDR solution
• Have IT professionals perform a thorough investigation of potentially compromised devices

Preventive Measures for the Future

Strengthen Your MFA Setup

• Use authenticator apps instead of SMS where possible
• Consider security keys like YubiKey or Titan Security Key for enhanced protection
• Enable number matching for Microsoft Authenticator to prevent MFA bombing attacks

Improve Security Awareness

• Learn to identify phishing attempts: Check sender addresses carefully, be wary of urgent requests, and verify unexpected messages through alternative channels
• Be suspicious of links: Hover over links to see the actual URL before clicking
• Verify website authenticity: Check for HTTPS and verify the domain before entering credentials

Implement Additional Security Measures

• Use a password manager to maintain unique, complex passwords
• Enable login alerts for your Microsoft account
• Regularly review account activity and security settings
• Consider Microsoft 365 Advanced Threat Protection for enhanced email security

For IT Administrators: Organizational Response

Immediate Actions

• Force password reset for the compromised account
• Temporarily block the account if necessary while investigating
• Review sign-in logs in the Azure AD admin center
• Check for unauthorized mailbox access through the Exchange admin center
• Analyze sent emails to identify potential phishing messages

Broader Protection Measures

• Review Conditional Access policies to restrict logins from unfamiliar locations
• Implement phishing-resistant MFA using FIDO2 security keys
• Deploy Microsoft Defender for Office 365 for enhanced protection
• Configure anti-phishing policies in the Exchange admin center
• Conduct regular security awareness training for all employees

Conclusion

Falling victim to a phishing attack can be alarming, but taking swift action can minimize the damage. Remember that having MFA enabled provides significant protection, but sophisticated attacks can still occur. By following the steps outlined in this guide, you can respond effectively to a Microsoft 365 account compromise and strengthen your security posture for the future.

For professional assistance with account recovery, security assessments, or implementing advanced Microsoft 365 security measures, contact Hexafusion's cybersecurity experts today.