Microsoft Defender detected and protected customers against a new software supply chain compromise affecting the "pytorch-lightning" package and immediately reported the issue to the repository maintainers for takedown: msft.it/6013vJisb. At the time the compromised packages were identified and distributed, Microsoft Defender had proactive detections that blocked the malicious files as Trojan:JS/ShaiWorm.DQ!MTB. For protected environments, Microsoft Defender for Endpoint raised the alert "ShaiWorm malware was prevented". Our assessment indicates that Microsoft continues to provide strong protection coverage and has prevented observed activity indicating attempts to install the modified packages. Microsoft Defender continues to monitor for potential follow-on activity, including suspicious use of potentially exposed cloud credentials across major cloud platforms. Observed activity remains limited to a small number of devices and appear contained to a narrow set of environments. We are also investigating container-based telemetry and registry-related signals that may indicate potential compromise in some scenarios. Microsoft continues to monitor and investigate the issue, with layered protections, broad prevention coverage, and ongoing hunting efforts in place. We will share updates as more information becomes available.