sharepoint Working with Managed Client Side Object Model (CSOM) Permissions. Breaking the security inheritance of a list
Example
string siteUrl = "http://MyServer/sites/MySiteCollection";
ClientContext oContext = new ClientContext(siteUrl);
SP.List oList = oContext.Web.Lists.GetByTitle("Announcements");
oList.BreakRoleInheritance(true, false);
oContext.ExecuteQuery();
