When your character reaches 500 reputation you are no longer protected from being backstabbed. The principle reason for getting killed by another player is when you expose yourself in recovery rooms and ammo stores. To minimize the risk of this happening you can get your own ammo store and recovery room. Be sure to set the "max reputation" in your recovery room/ammo store settings to slightly above your own reputation. This will prevent players with higher reputation entering your recovery room/ammo store. But remember, this is not completely safe because a players reputation is a combination of his strength, intelligence, tolerance and money but does not include other variables such as weapon, armor and equipment worn by user. Also be careful when accepting friend invites, this will grant them the opportunity to backstab you.