yes/no
Theres about 5 or 6 hundred systems in the game.
Each system has a security rating. Newbie systems are usually rated 1.0 (highest level of security). If you attack someone who you don't have kill rights on in .5-1.0 security, you get anally raped by NPC Concord (basically anti-PK guards) (with a longer response time depending on how low the security level is
.1-.4 has NPC guards which guard the NPC facilities (not concord, they only guard the stations and jumpgates) Also, they will occasionally help you if your attacked near a station and have a high standing with the station your nearby, the faction, and the NPC corp.
0.0 is basically privatly-owner sectors. as long as a player or corp has 4 "towers" (basically, small stations that have guns or utilities on them) in a system, they own the system.
I was in .4 security, and they used long-range scanning to detect me a really far distance away and then warp to me and blast me apart.
Anyway, back to sectors:
having towers (or what we call POS for privatly owned stations) in sectors is dangerous. They aren't "easily" destroied, but it happens fairly often by people with lots of firepower. It can take a few hours, but it happens eventually.
What a lot of the corps do (eve version of alliance), is put a bunch of POS's in a low-security sector and take control. Sometimes, they will control a lot of sectors (like goonfleet), and rent out empty space toa lliances.
Now, It's not like you just toss a station and let it go. You need fuel, minerals, and to be able to defend it when it's attacked. this takes a LOT of logistic planning. There are some corps that require members to donate a specific amount of fuel or minerals a month/week to make sure their stuff is operational. It's actually super-complicated running sectors.
Anyway, to conclude:
There are a few types of sectors:
High sec: .5-1.0
Low sec: .1-.4
and no sec: 0.0 (this has NO NPC guards at all)
I was in .4 sec (kinda risky, but the mish has like 200k in payout)