From Here: http://eve.grismar.net/security/

Security status and system security – EVE Online

Questions about this come up often in the help channel, so let me sum it up on an easy to remember URL :). If you want to read the official story out of game, try here.

If you think I got it wrong here, please let me know. Mail Grismar ingame. With negative standing, where can pilots travel?

Players with better than -2.0 can enter any system
Players with -2.0 or worse cannot enter 1.0 systems
Players with -2.5 or worse cannot enter 0.9 systems
Players with -3.0 or worse cannot enter 0.8 systems
Players with -3.5 or worse cannot enter 0.7 systems
Players with -4.0 or worse cannot enter 0.6 systems
Players with -4.5 or worse cannot enter 0.5 systems

Players with -5.0 or worse are considered outlaws. They can travel the same as any player with -4.5 or worse. Concord will not intervene if you try to kill outlaws and killing them does not lower your security status. Note however that this has nothing to do with bounties. Bounties on players are put there by other players. If you succeed in killing the player, you receive the reward, regardless of what you’re doing is legal. Concord completely ignores bounties. So when is it legal to kill someone?

In 1.0 - 0.5 systems, Concord will arrive on the scene and you lose security status
In 0.4 - 0.1 systems, Concord won't come, but you still lose security status
In 0.0 systems or below, nothing happens (see text below about 'below 0.0')