So... i can't find (or figure out) how does Piggyback or Accelerator work. So do i first use the offensive skill THEN start a hack or after ? Do i put the offensive program on the target i want to hack or on any colonized system in the path ?
I've put Accelerator on the system i have a Backdoor on and i saw NO change in the number of turns to hack my target, also put another on the target sysytem...but not change.

Please someone explain this.

Thank you for this well-thought-out answer it explained this very thoroughly. Thank you !

Could i ask about "Divert" ?

When my hack gets detected and the enemy starts the Trace, does Divert help me in any way ? Or is Divert just a tool i use when i change my mind ?

Divert can very effectively be used to mitigate the effect of a Trace, let me try and explain below. 

Let us assume that "System A" is the starting point of the hack and "System F" is the finishing point and there are Systems B, C, D and E in between them, thus my Hacking Operation looks like this:

System A -> System B -> System C -> System D -> System E -> System F

Let us then assume that my operation will take 10 turns to complete, one for each system and one for each jump between the systems. (It doesn't work like this but it will serve for the example). 

System A - - (Turn 1) - - > System B (Turn 2) - - (Turn 3) - - > System C (Turn 4) - - (Turn 5) - - > System D (Turn 6) - - (Turn 7) - - > System E (Turn 8) - - (Turn 9) - - > System F (Turn 10)

Let us then assume that your hack hits a Trace program at System D, which leaves you with 5 turns left on your operation (System D, jump, System E, jump, System F) The trace moves backward at 150% of the speed so it will only take 3 turns for them to get back to your origin point and shut down your operation. 

You can use Divert to change the destination point of your Hacking Operation to System D or E to reduce the time it takes for the operation to complete and thus bypass the Trace without having to cancel the operation and suffer the bandwidth penalty for doing so. If you Diver to System D then you will complete the operation next turn and therefore finish long before the Trace does. If you Divert to System E then you will finish in 3 turns just as the Trace program reaches your origin point. You will still finish the hack but it will be traced and you'll suffer the tracing penalties but not lose the bandwidth. 

Got it, crystal clear ! Tnx a lot for the explanation.

The reason i didn't figure it out by myself is...i always hacked the nearest system, so in that case there weren't any system in between my starting and target hack "string". So i couldn't Divert in a way that would be useful to me :)

Well now i understand that it's better to do some "long distant" hacks when you have divert.

It's important to remember that the "shortest path" is not always the "best path" when it comes to hacking. A Trace program has to follow the same route you followed to get to where you're going so the more jumps you have in your path the longer it will take the Trace to complete. If you assume worst case scenario and your opponent has an Encrypt program on the node you're trying to hack and it will take you around 4 turns to hack that system then you need enough jumps in your route to make the Trace program take longer than 4 turns to trace back to your origin point. In this case, a hacking path of at least six systems with a couple of your own Encrypt programs along the path will ensure you can finish the hack before the trace finds you.