Windows Defender Offline tool enables users to clean their systems of malware from a CD or other removable media. The tool is a throwback to the days of computing and viruses when the malware universe was small enough that all of the definitions to combat it could fit on a floppy disk. The new tool is currently in beta form, but it’s available for download from Microsoft s site now. Users would often have a rescue disk that could help them boot their PC in the event of a messy malware infestation.
Source: https://threatpost.com/microsoft-unveils-new-windows-defender-offline-tool-120911/75979/