Microsoft Security Essentials is now called Windows Defender. Security Essentials/Defender is a free antivirus/antimalware application provided by Microsoft. Prior to Windows 8 the application could be downloaded for free from Microsoft’s website. On Windows 8 and higher it comes free with the operating system.

Offline Updates for Microsoft Security Essentials

When someone bring me a computer and asks me to remove viruses and malware, the last thing I want to do is connect that computer to my network. This is a bit of a catch 22, since you need to be connected to the Internet to download antivirus software and updates. Luckily Microsoft provides an offline update file for Security Essentials that you can download from one computer and install on another.

Microsoft Security Essentials Definition Updates (x86)
Microsoft Security Essentials Definition Updates (x64)