The payment of salary or compensation to any person holding a position in the classified service is unlawful unless such person is certified by the State Civil Service Commission as lawfully employed in his position. Such certification may be made on an extended basis without time limitation or may be made for a limited period only. No further certification shall be necessary for the payment of compensation to such person so long as his status remains unchanged and during the stated limited period, if any. The Department of Civil Service shall examine the payroll of an agency at least once a year to determine that all persons listed on such payroll are employed in accordance with Civil Service Law and rules (Civil Service Law, section 100).