Multi-factor authentication (MFA) is one of the most important security controls a small business can enable. It stops many attacks where a criminal has obtained a password, and every business using Microsoft 365 should have it in place.
But MFA is not a magic shield. Attackers increasingly use convincing sign-in pages, repeated approval prompts and stolen browser sessions to get around it. For Cyber Awareness Month, here are seven practical steps SMEs can take to strengthen Microsoft 365 security beyond simply switching MFA on.
1. Move away from simple approval prompts
Older MFA methods can train users to press Approve without thinking. If someone receives repeated prompts they did not initiate, there is a risk they eventually approve one just to make it stop.
Use Microsoft Authenticator with number matching where appropriate. The sign-in screen displays a number that must be entered into the app, making an unexpected request much harder to approve accidentally. Staff should also know that an MFA prompt they did not initiate is a warning sign, not an inconvenience to dismiss.
2. Use Conditional Access to control sign-ins
Microsoft 365 can make access decisions based on more than a correct password and MFA response. Conditional Access policies can consider the user, device, location, application and level of risk before granting access.
For example, a business might require stronger authentication for administrators, block inappropriate legacy authentication, or require a compliant managed device before sensitive company information can be accessed. Policies need careful planning so legitimate users are not locked out, but they provide a valuable extra layer.
3. Protect administrator accounts separately
An administrator account is far more valuable to an attacker than a normal user account. If it is compromised, the attacker may be able to change security settings, create accounts or interfere with email and data.
Administrators should have separate accounts for administrative work rather than using privileged credentials for everyday email and web browsing. Strong MFA should be mandatory, and the number of privileged accounts should be kept to the minimum genuinely required.
4. Keep devices managed and patched
Account security and device security are closely linked. A perfectly configured Microsoft 365 account can still be exposed if the computer accessing it is infected, unpatched or shared inappropriately.
Business laptops should receive operating system and application updates promptly, use disk encryption and endpoint protection, and be monitored for security problems. Device management tools such as Microsoft Intune can help businesses apply consistent policies and identify devices that no longer meet the required standard.
5. Watch for stolen browser sessions
Modern attacks do not always try to steal just a password. Some phishing techniques attempt to capture an authenticated browser session after the victim has successfully completed MFA. This can allow an attacker to impersonate the user without repeatedly asking for a password or approval.
This is one reason staff awareness remains important even after MFA is deployed. Users should check addresses carefully before signing in, avoid following unexpected login links and report suspicious sign-in pages quickly. Security teams should also investigate unusual sign-in activity rather than assuming MFA makes every successful login trustworthy.
6. Review accounts and access regularly
Old accounts and unnecessary permissions create avoidable risk. When someone leaves the business, access should be removed promptly and active sessions revoked. Shared accounts should be avoided where possible because they make accountability and MFA more difficult.
Businesses should periodically review users, administrator roles, external guests, mailbox permissions and application access. It is much easier to spot something unusual when the environment contains only accounts and permissions that are genuinely needed.
7. Have a plan for a compromised account
Even good security controls cannot guarantee that an account will never be compromised. What matters is how quickly the business can respond.
A basic response plan should cover resetting credentials, revoking active sessions, checking MFA methods, reviewing mailbox forwarding and inbox rules, examining recent sign-ins and determining whether data or messages were accessed. If the compromised mailbox handles invoices or payments, customers and suppliers may also need to be warned about possible fraudulent messages.
MFA should be the starting point, not the finish line
For most small businesses, enabling MFA produces an immediate security improvement. The next step is to build layers around it: safer authentication, managed devices, sensible access policies, protected administrator accounts, monitoring and a clear response process.
ML Services helps businesses across Sussex secure and manage Microsoft 365, including MFA, Conditional Access, device management and ongoing account security. If you are unsure whether your Microsoft 365 setup has moved beyond the basics, contact ML Services for a practical review.