Virus signatures change daily. An offline update downloaded a week ago is already obsolete against "zero-day" threats. Always download the newest file right before you plan to use it.

You have multiple machines on a metered or slow connection and want to update them all using a single USB drive. Step-By-Step: How to Download Signatures Offline

Microsoft provides a dedicated portal for downloading the latest definition installers, known as Microsoft Defender Security Intelligence updates. 1. Identify Your System Architecture

You are managing high-security "air-gapped" computers that are never connected to a network.