What can be done to an offline POS?

I see a lot of POSes at moons that are anchored, but are not online (no shield bubble).
What can be done to these POSes? Are they abandoned? Can I steal them somehow? Or can I shoot them and destroy them? If they are offline, does it still take a very long time to destroy them?

• Just kill them all :)
• Maybe, maybe not. There are a lot of situation, when you haven't time to log in EVE and fill the fuel. After all real life is more important
• No, you can’t
• Yes, you can. But in high-sec you need declare official war on the owner, otherwise the police will intervene.  So it cost 50KK as minimum. In low/null just blow it up.
• It depend on what you’ll use for destroying. You can’t use dreadnought in highsec, so it'll take a lot of time in any case, if you haven’t big fleet of battle ships.

If it’s just tower – there are nothing valuable to pay 50KK or waste time and ammo. You should look for something like corp hangars, labs, silos, etc. If they have stuff inside, there is a 50% chance that stuff will drop when you destroy it!