In Webb v. Standard Oil Co. (1957) 49 Cal.2d 509, the California Supreme Court stated that inasmuch as the purpose of the statute is to encourage "a taxpayer to make full and truthful declarations in his return, without fear that his statements will be revealed or used against him for other purposes," the prohibition effectively creates a privilege, "and the privilege should not be nullified by permitting third parties to obtain the information by adopting the indirect procedure of demanding copies of the tax returns." The court applied the privilege to both state and federal income tax forms because "forcing disclosure of the information in the federal tax return would be equivalent to forcing disclosure of the state returns and would operate to defeat the purposes of the state statute." ( Id., at pp. 513-514.)