Referring to http://social.msdn.microsoft.com/Forums/en/sharepointdevelopment/thread/b73dd31b-1ec9-4f44-8cb2-80b2f6796eb5
Does SharePoint 2010 create default groups when site collection is created pro grammatically ?
You can use SPWeb.CreateDefaultAssociatedGroups method on your root web to create default Owner and Visitors groups.
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2 years ago