Saucer Attack! got my attention and many others in 1985 because of the amazing high resolution graphics for time. Here in this ad there is a side note from Jim Sachs claiming that the delay in the release of his next game ‘Time Crystal’ will have to be delayed because of the rampant copying in the C64 industry. They need this time to raise more capital and investigate more sophisticated protection techniques.
As for their Saucer Attack game the protection was ‘checks e11 on t5. tracks 5 and 35 are all e11 (id mismatch).’ Credits to: c64preservation.com