Mutual loan and building associations shall be exempt from the provisions of each and every law imposing taxes for state purposes on their capital stock or mortgages, and other securities for moneys loaned to their own members, but the real estate owned by said association shall be subject to the same rates of taxation as the real estate of other corporations and persons: Provided, however, That the right of the commonwealth to collect taxes already accrued is hereby reserved.
7 P.S. § 6030-1