I cant beat the challenge because my teammates don't help me and the enemy are hard to kill. And my rank is 20. i beat the first star itz the second that gets me. What are some strategies?
Start a new character and have him only do the one star before this. This way the enemy AI will not cap you as soon as you try and get to the hackbox. I got stuck on the 2 star as well until I did this. Finished it with plenty of time to spare.
This has been covered before. http://www.gamesas.com/index.php?/topic/1197944-be-more-objective-video-play-through-level-20-character-2-star-and-3-star/ I helped me, so its bound to do something for you.
Choose a mission thats primary objective is hacking:
[*]Plant the box, [*]start the hack, [*]bring progress to about 90 to 95%, [*]pull off the hack wait for enemy to come, [*]kill enemy, [*]disguise, [*]re-engage hack and complete [*]poof your new trophy!!
Ah T-stan already linked General Techniques guide. Check it out, and good luck! It is possible to beat every challenge with a lvl 20. (on 360 at least)