Listing All Active Directory Groups

Question

The following code lists some, but not all, Active Directory Groups. Why?

I am trying to list all security groups, distribution groups, computer groups etc. Have I

Answer 1

DirectoryEntry entry = new DirectoryEntry("ldap://ldap.gaurangjadia.com", "scott", "tiger");

DirectorySearcher dSearch = new DirectorySearcher(entry);
dSearch.Filter = "(&(objectClass=group))";
dSearch.SearchScope = SearchScope.Subtree;

SearchResultCollection results = dSearch.FindAll();

for (int i = 0; i < results.Count; i++) {
    DirectoryEntry de = results[i].GetDirectoryEntry();

    //TODO with "de"
}