(1) For purposes of this section, "tax information" means confidential income data and proprietary business information obtained by the department in the course of carrying out the duties now or hereafter imposed upon it in this title that has been communicated in confidence in connection with the assessment of property and that has not been publicly disseminated by the taxpayer, the disclosure of which would be either highly offensive to a reasonable person and not a legitimate concern to the public or would result in an unfair competitive disadvantage to the taxpayer.

(2) Tax information is confidential and privileged, and except as authorized by this section, neither the department nor any other person may disclose tax information.

(3) Subsection (2) of this section, however, does not prohibit the department from:

(a) Disclosing tax information to any county assessor or county treasurer;

(b) Disclosing tax information in a civil or criminal judicial proceeding or an administrative proceeding in respect to taxes or penalties imposed under this title or Title 82 RCW or in respect to assessment or valuation for tax purposes of the property to which the information or facts relate;

(c) Disclosing tax information with the written permission of the taxpayer;

(d) Disclosing tax information to the proper officer of the tax department of any state responsible for the imposition or collection of property taxes, or for the valuation of property for tax purposes, if the other state grants substantially similar privileges to the proper officers of this state;

(e) Disclosing tax information that is also maintained by another Washington state or local governmental agency as a public record available for inspection and copying under chapter 42.56 RCW or is a document maintained by a court of record not otherwise prohibited from disclosure;

(f) Disclosing tax information to a peace officer as defined in RCW 9A.04.110 or county prosecutor, for official purposes. The disclosure may be made only in response to a search warrant, subpoena, or other court order, unless the disclosure is for the purpose of criminal tax enforcement. A peace officer or county prosecutor who receives the tax information may disclose the tax information only for use in the investigation and a related court proceeding, or in the court proceeding for which the tax information originally was sought; or

(g) Disclosing information otherwise available under chapter 42.56 RCW.

(4) A violation of this section constitutes a gross misdemeanor.