There were a few Discussions about that, in the german board.
As far as I know (I never tested it. I read it in this board):
- Islands with a level greater than 13 can loose island tiles.
- The chance drops with the island-size of your victim (so you nead more islandbreakers to increase the chance, or more attacks to get island tiles).
- When an island size is - irrespective of its level - lower or equal as 121, its impossible to break tiles from that island (even the tiles in the store are secure, then).
On old worlds, there were a few different rules. But I think hel has the "new regulation".
Thats the best (up-to-date) source I could find (translated to english by google):
http://translate.google.at/translate?hl=…855%23post92855
Ps
Mh.. Need to write more english texts... My english sucks...