Microsoft Excel to Block Risky File Types by Default

Microsoft Excel is tightening its security measures to protect users from potential threats. Starting in October 2025, Excel will block external workbook links that point to unsupported or high-risk file types. If you rely on linked workbooks for data updates, these files may either fail to refresh or display the #BLOCKED error. This update is part of Microsoft’s ongoing effort to make Excel safer for both personal and business use.

Why Microsoft Excel is Blocking File Types

This change is designed to reduce the risk of malicious attacks through external files. Excel’s Trust Center already flags certain file types as unsafe, but now the software will actively block them by default. Unsupported file types can be exploited by cybercriminals to gain indirect access to sensitive data. With this update, any risky external links will automatically be disabled, and users will see a business-bar warning in Excel before attempting to interact with these files.

What Happens When Excel Detects Blocked Files

Once this policy is active, Excel will prevent new or refreshed links from working if they point to blocked file types. Affected workbooks will either fail to update or show the #BLOCKED error, alerting users that the link is unsafe. Microsoft has confirmed that this behavior will start with Build 2510 if the policy is not manually configured by administrators or users. The change emphasizes proactive security, ensuring that risky files don’t compromise data integrity.

How to Stay Safe and Prepare for Excel Changes

To avoid disruption, users should review any existing external workbook links and remove or replace connections to unsupported file types. IT admins can adjust policy settings in Excel if certain files are necessary for internal workflows. Microsoft also recommends keeping Excel updated to the latest build to benefit from all security patches and new safety features. By preparing ahead, businesses can maintain smooth operations without risking exposure to malicious files.