@s{quotedtext}
@s{quotedtext}
A real crash.
In a perfect world, Bitcoin version 0.1 would have included code that looked for a "Bitcoin version X or later required to read this wallet.dat file" setting, and notify the user and exit cleanly if X is greater than the version you're running.
We don't live in a perfect world.
So the second-best solution was to have version 0.4 and later do the "Bitcoin version X or later required to read this wallet.dat file" thing. And write a value into the wallet that causes previous versions of bitcoin to crash on startup.
If previous versions didn't crash when given an encrypted wallet, they'd just ignore the encrypted keys, generate a bunch of new, unencrypted keys, and give people heart attacks when they ran the old version of bitcoin and told them they had a 0 bitcoin balance.