Active directory users

using (DirectoryEntry domain = new DirectoryEntry("LDAP://" + domainToBeSearched))
{
    using (DirectorySearcher searcher = new DirectorySearcher())
    {
        //Set root for searching
        searcher.SearchRoot = domain;
        //Set filters for searching user
        searcher.Filter = FormFilter("user", userName + "*");
        searcher.SearchScope = SearchScope.Subtree;
        searcher.PageSize = 10;
        //Get all registered user on basis of passed filter
        using (SearchResultCollection adResult = searcher.FindAll())
        {
            DataRow dtrUsers = null;
            foreach (SearchResult result in adResult)
            {
                if (dtUsers.Select("key='" + result.Properties["samaccountname"][0].ToString() + "'").Length <= 0)
                {
                    //Add user to datatable
                    dtrUsers = dtUsers.NewRow();
                    dtrUsers[0] = result.Properties["samaccountname"][0].ToString();
                    dtrUsers[1] = result.Properties["DisplayName"][0];
                    dtUsers.Rows.Add(dtrUsers);
                }

            }
        }
    }
}