[anovikov]

If the Enigma machines were operated properly, they could never be broken. Breaking them were a result of German lack of discipline and irresponsibility, not machine's weakness (maybe a simple inscription on the cover of machine in the bold letters would help though, machine designers just expected too much from their enlisted, barely literate operators).

[gshubert17]

Not never. One of the "features" of the Enigma was that a plaintext letter could never be encrypted to itself. An 'A' going in could come out as any other letter, except 'A'. German information security policies were generally pretty good. There were lapses, of course, and some of these were used to form cribs for a known plaintext attack on encrypted messages. But Enigma was/is not invulnerable.

People found a couple encrypted Enigma messages after World War II. Here is a note from a group of people using modern computers and brute force to decrypt them:

http://www.enigmaathome.net/forum_thread.php?id=318

[anovikov]

yes of course, by 'never' i mean 'not in the WWII timeframe'.