Stealing in general is illegal. Bitcoins? Ofcourse. It's a currency. It's stealing money basically.
Only difference is chances of your getting caught is less with Bitcoin.That is why bitcoin should be used with much care a needs to kept safely
Yeah indeed. Ofcourse stealing bitcoin is illegal cause taking anything which isn't yours without permission is illegal. BUT they can't really catch you so easily cause bitcoin is so anonymous so it's the perfect crime but still it's a crime.
It seems a lot of you guys are answering the question from the header directly, you should read op's scenario. I don't think it's stealing because in his scenario he didn't plan to take anyone's Bitcoins. He merely created a new address and found Bitcoins in it, he didn't 'steal' them, he got them because of some glitch. In a case like this I would totally keep the coins for myself

I think people do not see the contents topic of OP, people only look at the title of this topic only
I think it is impossible that there bitcoin is ready for a new bitcoin address created, even you can not send bitcoin to any address ?
so I think it is impossible to obtain bitcoin simply create an address Lol