Mont. Code Ann. § 27-18-408

Judgments standing in favor of and in the name of the defendant upon the records of the clerk of the district court must be attached by leaving with the said clerk of the district court a copy of the writ and a notice stating that the said judgment is attached in pursuance of such writ. The clerk of the district court must index and keep a record of all attachments of judgments thereunder, and such attachment is binding on the judgment creditor.