Your just sitting there and you get a notification that you have received 20 bitcoins out of nowhere. What would you do?
I would search the forum to see who has sent it mistakenly to me (because there is no other reason why someone would send me 20 bitcoins
![Cheesy](https://bitcointalk.org/Smileys/default/cheesy.gif)
). I will ask them to sign a message with the sending address to confirm that it was theirs. And I would send them back their bitcoins.