“Sometimes, malicious and other potentially unwanted software, including rootkits, try to install themselves on your PC. This can happen when you connect to the Internet or install some programs from a CD, DVD, or other media. Once on your PC, this software might run immediately, or it might run at unexpected times. Windows Defender Offline Beta can help remove such hard to find malicious and potentially unwanted programs using definitions that recognize threats. Definitions are files that provide an encyclopedia of potential software threats. Because new threats appear daily, it's important to always have the most up-to-date definitions installed in Windows Defender Offline Beta. Armed with definition files, Windows Defender Offline Beta can detect malicious and potentially unwanted software, and then notify you of the risks.
To use Windows Defender Offline Beta, you need to follow four basic steps:
Download Windows Defender Offline Beta and create a CD, DVD, or USB flash drive.
Restart your PC using the Windows Defender Offline Beta media.
Scan your PC for malicious and other potentially unwanted software.
Remove any malware that is found from your PC.
Windows Defender Offline Beta will walk you through the details of these four steps when you're using the tool. If you've been prompted in Microsoft Security Essentials or Windows Defender to download and run Windows Defender Offline Beta, it's important that you do so, to make sure that your data and your PC isn't compromised.
To get started, find a blank CD, DVD, or USB flash drive with at least 250 MB of free space and then download and run the tool—the tool will help you create the removable media.”