The system of pre-defining the indicator setting for the day for all Enigma operators on a given network, on which the method of characteristics depended, was changed on 15 September 1938. The one exception to this was the network used by the "Sicherheitsdienst" (SD)—the intelligence agency of the SS and the Nazi Party—who did not make the change until 1 July 1939. Operators now chose their own indicator setting. However, the insecure procedure of sending the enciphered message key twice, remained in use, and it was quickly exploited. Henryk Zygalski devised a manual method that used 26 perforated sheets, and Marian Rejewski commissioned the AVA company to produce the "bomba kryptologiczna" (cryptologic bomb).