Like any theory in LOST, this will probably soon be proven wrong, but isn't the theorizing part of the fun? So here goes:
Jacob needs to recruit people as candidates. As long as there is a candidate MIB is trapped. Jacob wants to keep his candidates safe, so in the process his touch protects them and also guides them to the island. Jacob's touch is potent, and pretty much insures their safety. But the "loophole" in a candidates protection is that they can only be killed by another candidate. MIB can't kill any of the candidates by his own actions, but can try and manipulate them by "infecting" them. MIB had Ben kill Jacob, Linus (117) was a candidate and could kill Jacob. Richard told FLocke "that only the leader can request and audience with Jacob, and there can only be one leader at a time." I think this was a clause set forth by Jacob to make sure the MIB wasn't controlling someone into killing Jacob.
So here goes a list of some of our characters and who killed them. Since we don't know the names of all 360 candidates, I'm assuming that some of these people were candidates. Now maybe there is also a clause that states Candidates can't be killed by another candidate unless they killed a candidate themself. This is why Locke didn't die in the Pit after Ben shot him. But when Locke killed Naomi (27) then he became fair game. As long as our candidates don't kill another candidate, they are safe...
I'm mainly only listing people that have a connection to names we've already seen listed.
Lacombe (2) infected by Smokey killed by Rousseau (20)
Locke (4) killed by Linus (117)
Pryce (14) killed by Reyes (8)
Rousseau (20) killed by Keamy? (not known candidate)
Dorrit (27) Killed by Locke (4)
Rutherford (32) - Cortez (not known candidate)
Brennan (35) infected by Smokey Killed by Rousseau (20)
Stanhope (goodwin) (48) Killed by Cortez (not known candidate)
Burke (julliet) (58) - ? Jacob?
Burke (edmond) (58) - Killed by Jacob?
Troupe (90) killed by Jacob?
Faraday (101) Killed by Hawking (not known candidate)
Montand (102) infected by Smokey Killed by ? (maybe research team?)
Lewis (103) (Charlotte?) - ?
Lewis (103) (David?) killed by Purge?
Friendly (109) killed by Ford (15)
Linus (117) healed by Jacob (maybe no longer a candidate?)
Dawson (124) - Released by island?
Straume (171) - ?
Pace (195) - killed by Mikhail (maybe MIB?)
Carlyle (226) - Killed by Locke (4) indirectly
Jenkins (285) - ?
Mars (301) Attempted by Ford (15) but killed by Jack (23)
Littleton (313) infected by Smokey
Henderson (335) (rose?) - ?
Martin (337) (Carl) - Keamy (not a known candidate)
Chang - Purge?
Pickett (Danny) - killed by Burke (58)
Pickett (colleen) - Killed by Kwon (42)
Goodspeed (Horace) - Purge?
Goodspeed (Ethan) - Killed by Pace (195)
Sullivan - ?
Cortez (not a known candidate) killed by Dawson (124)
Smith (libby) (not a known candidate) killed by Dawson (124)
Keamy (not a known candidate) Killed by Linus (117)