Locking onto an enemy one on one is fine but when I fight more than one enemy the game locks onto one enemy automatically and it makes combat really difficult. Is there any way to stop this from happening?

I only find that a problem with ranged fire - it keeps changing the lock and often is NOT the closest too you. For close in fighting, I think all that is needed is to pint (with the mouse) at the enemy you want to hack and it will be the target.