A new tool called BigDiskBuster has been uncovered, which can interfere with Microsoft Defender's ability to update its virus detection database. This could leave computers more vulnerable to the latest cyber threats. The tool is associated with a proof of concept (PoC) developed by a group known as Nightmare Eclipse. While it doesn't directly disable Defender, it prevents the software from downloading and installing critical updates and new antivirus signatures, which are essential for identifying and blocking new threats. According to one report, the method used by BigDiskBuster involves creating hidden temporary files that take up free disk space. This action limits the space available for Defender to install updates. Once the update fails, these files are closed, and the disk space is freed up again. This cycle repeats, potentially blocking updates until the next attempt. Another report adds that the PoC also interferes with MRT.exe, a Microsoft tool used to remove malicious software, by keeping access to a file that could prevent its replacement. While Defender continues to monitor the system in real time, its ability to detect new threats may be limited if the updates are blocked. It is important to note that BigDiskBuster does not allow remote access to a machine. For it to work, the program must already be running on the device, making it a local attack that requires an initial compromise. While this does not mean the risk is insignificant, the PoC is now public, which means it could be reused, modified, or incorporated into future attacks. This tool is seen as the successor to UnDefend, a similar tool revealed earlier this year, and it highlights the ongoing conflict between Nightmare Eclipse and Microsoft, which has been ongoing for several months. The researcher behind the PoC criticized Microsoft for its handling of reported vulnerabilities and chose to disclose the findings before a patch was released. This approach is inherently risky because it could allow malicious actors to exploit the vulnerabilities. However, in the past, several vulnerabilities disclosed by Nightmare Eclipse have been quickly addressed by Microsoft. For BigDiskBuster, however, the company has not yet issued a public response or patch.