Answer from cs61c-cj (Peter Lau 16539384) for Question 1
If data can be represented as anything, then a clever programmer can modify data to his or her liking, legally or illegally.  Instructions can be easily changed and modified to the programmer's liking.  For example, if we wanted to change how a certain MIPS program ran, we could modify where $ra jumps for a certain loop.  One possible technique to prevent this might be to insert checksum instructions regularly in the code that would check the integrity of nearby instructions.  This would slow the machine down though, since it has to calculate these checksums.