Cheating on Khan Academy assignments

1) How can I tell when a student cheats?

2) This spring when I asked one of my freshmen how she was able to finish a home work assignment so quickly she said, "I used scripts!"  She did not seem to be aware that this was problematic! How can I tell when this and other forms of cheating are happening? How can I minimize it?

3) This year I had several occasions where a student claimed to have completed their assignment but there the scores on my teacher dashboard were all 0's. When I Google researched a bit about running scripts to cheat in Khan Academy I saw something that I interpreted as saying that Khan Academy does not record an exercise as complete if it detects certain types of cheating. I am not very computer literate and my interpretation could be way off the mark. Please help me understand more.