Well number two if a bad guy can alter the operating system on your computer it's not your computer
anymore.
You should be aware that the operating system basically controls the computer.
This means that many system processes are not in any way controlled or supervised.
For instance this is how kernel drivers work kernel processes cannot be supervised by the operating
system itself.
To achieve that such supervision must take place in the kernel mode and this would allow a hostile process
to gain control over the kernel.
It's a universal principle which is true for all operating system.
You should also remember that operating systems are characterized by high complexity and a large hard
drive footprint.
Newer versions of Windows take up about 10 gigabytes of space and consist of around 60000 files.
Some of those files are very rarely used
in the slide you can see an example of such a file Edlin DXi from Windows Vista.
It's safe to assume that few people knew that this file existed in Windows Vista Edlin is a command
line editor worldwide.
It was only used five times.
Nevertheless it's still a part of the system as you can see the permission inchers list is very restrictive.
Only a trusted installer can modify the file other users can only execute and read it.
The file is protected but if it was modified you wouldn't learn about it.
The protection of all system files would be very costly if someone managed to modify the file Edlund
DXi it would mean that the person had trusted installer permission.
The person who managed to obtain that kind of permission could easily cover up their actions as well.
The situation persists even though operating systems protect the integrity of their components.
For example if you accidentally or purposefully delete some files you can benefit from automatic file
recovery.
Also there is a system process that prevents all users except the trusted installer from overwriting
deleted files.
If these mechanisms were defeated you could no longer trust any component of the system.
The second law is still valid despite all the security solutions we've discussed before.