may be transmitted as line 32. The VideoCrypt-S variant used six blocks of forty seven lines per field. It had three scrambling formats: full shuffle in which 282 lines were affected; half shuffle, in which every alternate field was scrambled; and a line delay scramble in which the start position of the video in each line was pseudo-randomly delayed. The BBC chose to use line shuffle scrambling rather than line cut-and-rotate because tests had shown that line cut-and-rotate is more susceptible to picture degradation when exposed to ghosting and co-channel interference conditions commonly present in terrestrial transmissions. Attacks The VideoCrypt system was far from secure and a number of hacks were employed. Card attacks Hackers discovered methods of preventing Sky from killing or deactivating their cards. The simplest of these attacks relied on the fact that Sky was using EPROM technology for its smartcards at the time. Thus by modifying the decoder to limit the write voltage to the card, it was possible to stop cards being turned off over the air. Another, known as the KENtucky Fried Chip attack relied on replacing the microcontroller that controlled the smartcard to decoder interface. This attack relied on blocking packets with the smartcard's identification number. The voltage based attack failed after Sky changed to smartcards that used EEPROM technology. Commercial pirates completely reverse engineered the Sky smartcard, removed the access control routines and created working pirate smartcards using different microcontroller types (typically the PIC16C84) from that used by Sky. Hackers also discovered (after the commercial pirate code became public) ways of switching on "dead" cards using a computer and smartcard interface by sending a properly formatted and addressed activation packet to the card. Variations on this attack also allowed existing subscriber cards to be upgraded to more expensive subscription packages. This attack was known as the "Phoenix Hack" after the mythical bird that could bring itself back to life. Datastream attacks Other successful hacks involved sampling the datastream between the card and the decoder, for example you could record a movie and store the decoder information so that people could then use it to decode the same movie that they recorded earlier with a decoder and "dummy" card (the dummy smartcard was an interface that received the synchronised decryption seeds from a computer). The attack was known as the Delayed Data Transfer hack and it worked because the conditional access data, decoder