1. There are well established algorithms (e.g., SHA) that can take a file and produce a unique numeric value (a checksum or hash digest).The sha sum for a file will be different if even one byte of that file changes. A bad guy might attempt to modify a system configuration file (i.e., one that does not often change) in a way that goes undetected. If the attempt to modify the file goes undetected (e.g., an inside job might not be seen as a violation), how can a system operator check on the integrity of files? There are commercial products and services that can be used to help you monitor the integrity of your files: name one.

2. Read the article Reflections on Trusting Trust by Ken Thompson (one of the creators of UNIX) and answer:

https://www.ece.cmu.edu/~ganger/712.fall02/papers/p761-thompson.pdf

(a) What two hacks did he introduce? Why did he need both of them?

(b) Has the Ken Thompson Hack (KTH) been eradicated, or have there been more recent cases of it?

(c) What impact does the KTH have if it turns out to be widespread (i.e., not the specific program that he used, but applying the hack to other programs)?