Following commands disables Microsoft AutoUpdate launch agent from launching at boot and periodicaly checking for updates.
sudo defaults write /Library/LaunchAgents/com.microsoft.update.agent.plist Disabled -bool YES
sudo defaults write /Library/LaunchAgents/com.microsoft.update.agent.plist RunAtLoad -bool NO
sudo chflags schg /Library/LaunchAgents/com.microsoft.update.agent.plist