Master Browser?

Go to Control Panel>Networks. To set or check the browser settings, scroll the network Configuration for File and printer sharing for Microsoft Networks. Highlight this entry and click the Properties button. Select Browse Master and choose from Disabled, Enabled, or Automatic.

Also see:

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http://makeashorterlink.com/?Y2BC12371

http://makeashorterlink.com/?L3EC25371

When a computer starts and the value of the MaintainServerList entry in its registry is set to Auto, the master browser is responsible for telling the system whether or not to become a backup browser.
If the registry of a computer has the value of the MaintainServerList entry set to Yes, the computer is a backup browser for the domain or TCP/IP subnet.
Therefore, set the value of the MaintainServerList to NO and it will stop