It really isn't all that difficult to remain undetected with the all the upgraded powers. I just got done with the Boyle mission and I have not bee detected in any of the missions. As long as you use stop time liberally and kill/knock out and remember to check your corners you should be fine.
If you stay in stop time mode you can get infinite fatalities. Since they aren't fighting back you get a fatality on them every time.
firewall and other security software.
on trainer and game.
version and distribution.