As pointed out by haileris, Today I have added one more rule to block C:\Program Files\Microsoft Security Client\Antimalware\MpCmdRun.exe , Let's see if this works.
Oh No! the MSE updated again despite my firewall rule, Can u see where I went wrong. Am I right in blocking msseces.exe or there is another program which is responsible for update.
And yes as pointed by bigdogchris it would be required to regularly download Definitions from http://anonym.to/http://www.microsoft.com/security/portal/Definitions/ADL.aspx
I too wanted to disable Auto Update due to data volume plan (1GB). I googled and found some registry changes and some I tried on my own, but none worked (may be I wasn't able to configure it properly) but then the following trick worked.
I created a firewall rule which blocks Microsoft Security...