Answer from cs61c-ax (Amanda Alfonso 15906918) for Question 1
A possible way to exploit a security hole is by using overflow.  Computers must be certain to check for overflow/underflow when doing math; if someone were able to cause overflows in computer operations it could completely alter the performance - especially since data is often in the form of numbers (be them integers, floats, etc).  One possible (though horribly unreasonable) technique to prevent this would be to disallow negative numbers; of course, the terrible tradeoff would be disallowing negative numbers (hehe), which would also severely limit the power and range of uses of a computer.