Me too! I must of tried this 4 times now with my level 19 character! It is extremely frustrating how your friendly AI stands by as the engineers destroy the hack box. I have only completed it once but was killed whilst trying to deliver the intel. I recommend trying to plant it and then hide back where your command post is.
When i get my Bulpdaun i will parade it proudly.
2 Star Be More Objective solo nearly impossible with Light body type
Once you plant the hack box, you have to walk around the corner to where the command post is and safely hack from there. Just pray an engineer doesnt go and de-hack it. Thats how I did it, took me about 20 tries though.
wathc this vid http://www.youtube.com/watch?v=SO_N6tXmu4Y&feature=channel_video_title
i personally found all challenges easy :S , easiest tactic is go heavy and spam the GL
I finally finished this with a medium character. I immediately sprinted to plant the HE device, ran to cover with a nade primed, took out as many enemies as I could and focused on medics when I could spot them amidst all the frantic targeting I was doing. When I got to the engineer part I fortunately was able to place a medium turret by the machine I had to repair to keep the enemies more busy. When I finished that and got to the operative part I managed to take out the entire wave of enemies after a long firefight and had just enough time to plant the hack device. As soon as I could I strafed to the command post as I was hacking and made it to around 40% then an enemy engineer started to reverse my effort. I again got lucky and my AI teammates for once helped me out and killed the engineer and I made it to 100%. I go around, climb up and drop down to get the briefcase and like a bat out of hell I sprinted toward my spawn area and hopped on the boxes and over the railing and made my way to the final point and only had one enemy in my way to try to stop me. I spammed the **** out of em and finished it with a couple minutes to spare.
I would say I did this with 20% skill, 20% rage, and 60% luck.
You guys know it, but I just want to remind you: gibbing is important too. Put them down, and make sure they stay down.

The Guide recommends doing them with 0 level characters first to unlock the gear and then try them with your higher level characters to achieve better times.