Hehe, I'm going to upload a commentary on this exact issue either tomorrow or monday. Already captured the video for it yesterday. :laugh:
1. What level are you? higher level player = smarter enemy bots = harder challenge. Try it with a fresh character, it WILL be easier.
The bots aren't actually Smarter, they just use more "hacks" to detect you and your team, while your team doesn't step up their game at all.
(I think the bots work almost identical to the ones from Counter-Strike Source.)
2. Try out different body types and weapon combos. I was level 9 and hadn't heard about point 1 when I first did the challenge you're stuck on. I couldn't even get close to finishing the hacking objective when I was a Light Operative
Tried Medium, but still no hope. As a Heavy, at level 9, I finally got it.
I was between 7 & 8 and tried it with the Heavy, the Light and the Medium. Didn't manage to get anywhere close 75% for hacking...
The bots can tear you apart across half the map, even if you're a Heavy.
The Engineer-Objective isn't so hard to do if you have the turret-ability, btw. I used both a turret and a mine and managed to finish that one quite fast.