well good for you if got its private key. well its stealing though, i just feel sorry to the one you stole the bitcoins. haha. well thats life, theres a hacker and theres someone who got hacked. then cycle again. but if its by accident or you receive funds on a random address. it luck!

it its luck if you got fund accidentally, but it will more good if you return the fund to the person who sent you the fund accidentally because he will not be feeling good, and will be in tensing for losing his money.