Change Microsoft Security Essentials Update Frequency

1. "C:\Program Files\Microsoft Security Client\Antimalware\MpCmdRun.exe -SignatureUpdate "

http://www.techrena.net/windows/change-microsoft-security-essentials-update-frequency/

2. http://www.mydigitallife.info/fix-microsoft-security-essentials-mse-not-auto-update-virus-and-spyware-definitions-signature-problem/

Run Registry Editor (RegEdit).
Navigate to the following registry key:
HKEY_LOCAL_MACHINE/Software/Microsoft/Microsoft Antimalware/Signature Updates

In the right pane, take ownership and grant full control permissions on a registry key, a REG_DWORD value named SignatureUpdateInterval.
Double click on the SignatureUpdateInterval. By default, its value is 24 (in Decimal) or 18 (in Hexadecimal). Change its value to any number between 1 and 24 (both inclusive) in Decimal.
The numerical value determines how frequent and how fast (in hours) Microsoft Security Essentials will check for updates and update the virus and spyware definitions.

Restart the computer.