Persistencia.Conexao.executeReader C# (CSharp) Method

        public SqlDataReader executeReader(String SQL)
        {
            SqlCommand cmd = cn.CreateCommand();
            cmd.CommandText = SQL;
            return cmd.ExecuteReader();
        }

        public void logar(String usuario, String senha)
        {
            String SQL = "SELECT * FROM dbo.CadLogin WHERE usuario = '" + usuario + "'  AND senha= '" + senha + "'";
            Conexao oConexao = new Conexao("SQLServer");

            SqlDataReader dr = oConexao.executeReader(SQL);

            while (dr.Read())
            {
                this.idCadLogin = Convert.ToString(dr["idCadLogin"]);
            }
            dr.Close();

            oConexao.fechaConexao();
        }