Microsoft has recently announced a new security measure for its Excel spreadsheet software, aimed at improving user security around the world. In the past, macros in Office files were commonly used to deploy malware to target endpoints, prompting Microsoft to block all macros in Office files downloaded from the internet. Since then, hackers have been experimenting with alternative methods to deliver malware payloads, and one methodology that has grown in popularity is the use of XLL add-ins.
XLL files are DLLs that Excel users can add to expand the program’s functionalities with things like custom functions, dialog boxes, or toolbars. They have become the next best way to deploy malware after macros, making them a popular choice for hackers. In response to this, Microsoft has made a significant change to Excel’s security by blocking all untrusted XLL add-ins by default in Microsoft 365 tenants worldwide.
This change was first announced in early January and was added to the Microsoft 365 roadmap. It was then rolled out to Insiders for testing. Now, two months later, the feature is being rolled out to all other users. By late March, all desktop users in the Current, Monthly Enterprise, and Semi-Annual Enterprise channels should have this extra layer of protection.
According to Microsoft, “We are introducing a default change for Excel Windows desktop apps that run XLL add-ins: XLL add-ins from untrusted locations will now be blocked by default. We have already completed rolling out to Insiders preview. We will begin rolling out early March and expect to complete by late March.” After the change is complete, users will be notified when trying to run XLL-powered content coming in from an untrusted location. The notification will explain what the potential risks are and provide more information on how to stay safe.
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Once the update rolls out, it is likely that delivering malware with shortcut files (.LNK) will become even more popular. Therefore, it is important to stay vigilant and cautious when downloading and opening files from unknown sources.
Microsoft’s new security measure for Excel is a much-needed improvement that will help protect users from malware attacks. By blocking untrusted XLL add-ins by default, Excel users can rest assured that they are better protected against potential threats. It is important to stay up-to-date with the latest security measures and to exercise caution when downloading and opening files from unknown sources to ensure your safety online.