Similar to all Microsoft products, Microsoft Security Essentials (MSE) also uses Windows Update for updating its virus definitions as well as program modules. It is very helpful that we don’t need to take much attention on the update, i.e. it will be automatically updated when an internet connectivity is available.
What will happen if there is no internet connectivity in a PC ? the update process will not take place. It may cause new malwares attack our PC. There is the importance of an Offline Updater. Microsoft offers Standalone Offline virus definition updates for Microsoft Security Essentials.
I am sharing the download links of official offline updates here:
Download MSE Virus Definitions (x86)
Download MSE Virus Definitions (x64)
After downloading the package, run it with Administrative privileges and it will install the latest virus definition updates!