Phishing Risks in Microsoft 365: Essential Checks to Protect Client Data
Phishing remains the most common cyber threat facing regulated firms today. It is an ongoing operational risk that can impact your firm's reputation, client trust, and compliance status. With Microsoft 365 widely used in accountancy, legal, and financial services, understanding why phishing is so persistent and what you can do to reduce the risk is critical.
This post explains why phishing continues to thrive, how AI is making scams more convincing, why Microsoft 365 accounts are prime targets, and what practical steps you should take now to protect your firm and client data.
Why Phishing Is Still So Common
Phishing attacks keep succeeding because they exploit human nature and everyday business processes. Attackers send emails that look legitimate, often mimicking trusted contacts or brands. Many phishing emails ask recipients to click links, download files, or provide login details.
Regulated firms are especially vulnerable because:
You handle sensitive client data that criminals want.
Your teams regularly exchange confidential information by email.
Compliance requirements mean you store valuable records in Microsoft 365.
Staff may be busy and less likely to spot subtle signs of phishing.
Phishing is a low-cost, high-reward tactic for attackers. They only need one employee to fall for a scam to gain access to your systems. This makes phishing a persistent threat that requires ongoing attention.
How AI Makes Phishing Emails More Convincing
Artificial intelligence tools have changed the phishing landscape. Attackers now use AI to craft emails that are harder to detect:
Personalised messages based on publicly available information or leaked data.
Improved language quality that avoids typical spelling or grammar mistakes.
Context-aware content that fits your firm’s industry or recent events.
Deepfake audio or video to impersonate executives or clients.
These AI-assisted scams can fool even experienced users by mimicking writing styles and creating believable scenarios. This raises the stakes for regulated firms, where a single compromised email can lead to data breaches or regulatory penalties.
Why Microsoft 365 Accounts Are Attractive Targets
Microsoft 365 is the backbone of many regulated firms’ communication and collaboration. Attackers target these accounts because:
They provide access to email, calendars, files, and contacts.
Compromised accounts can be used to send phishing emails internally, increasing trust.
Attackers can access sensitive client data stored in OneDrive or SharePoint.
Microsoft 365 accounts often have privileged admin roles that control security settings.
A successful breach can lead to data theft, fraud, or disruption of business operations. Because Microsoft 365 integrates with many other tools, the impact can spread quickly.
The Client Data and Compliance Risks of a Compromised Mailbox
When an attacker gains access to a mailbox, the consequences go beyond just stolen emails:
Client confidentiality is breached, risking reputational damage.
Sensitive documents can be copied, deleted, or altered.
Regulatory requirements such as GDPR or financial regulations may be violated.
Your firm could face fines, investigations, or loss of professional licenses.
Incident response and recovery can be costly and time-consuming.
For regulated firms, protecting client data is not optional. It is a core part of your duty of care and compliance obligations.
Practical Checks Firms Should Make Now
You can reduce phishing risks by focusing on key Microsoft 365 security controls and staff awareness. Here are practical steps to take immediately:
Check Multi-Factor Authentication (MFA) coverage
Ensure MFA is enabled for all users, especially those with admin privileges. MFA blocks attackers even if passwords are stolen.
Review Conditional Access policies
Use conditional access to restrict login locations, devices, or risk levels. This limits where and how accounts can be accessed.
Audit admin accounts
Confirm that only necessary users have admin rights. Remove or reduce privileges for accounts no longer in use.
Inspect mailbox rules and forwarding
Attackers often create hidden rules to forward emails externally. Regularly review and remove suspicious rules.
Disable legacy authentication protocols
Older protocols bypass modern security controls and are commonly exploited. Disable them unless absolutely required.
Encourage staff to report suspicious emails
Build a culture where employees feel comfortable reporting phishing attempts without fear of blame.
Verify backup and recovery processes
Ensure you have reliable backups of emails and files to recover quickly after an incident.
Test your incident response plan
Run tabletop exercises to prepare your team for a phishing breach scenario.
What to Check First
To start strengthening your defences today, focus on these actions:
Confirm MFA is active for all users, especially admins.
Review mailbox rules for any unusual forwarding or filters.
Disable legacy authentication protocols in your Microsoft 365 tenant.
Ensure your staff know how to spot and report phishing emails.
Verify backups are current and tested for recovery.
Taking these steps will significantly reduce your risk of a phishing breach and help protect your clients’ data.
