Oregon Revised Statutes Revenue and Taxation § 314.407

(1) In the case of a return submitted to the Department of Revenue with payment of less than the amount of tax computed to be due, the difference between the tax computed to be owing by the taxpayer and the tax submitted with the return is considered as “assessed” on the due date of the return (determined with regard to any extension of time granted for the filing of the return) or the date the return is filed, whichever is later.

(2) The term “time of assessment” means:

(3) Unless a warrant has been recorded in the County Clerk Lien Record in the county in which property is located, no warrant shall be considered as a lien with respect to that property.