Today at night Enigma@Home server received a full decrypt of FNYG MXHU message.
At 76 letters length it is probably the shortest known M4 message broken by 'ciphertext only' attack.
The project made 48 full walks through the full M4 Enigma keyspace before the solution was found. I don't have full CPU-time stats yet, but I doubt this could be done on a single PC in reasonable time.

The message was one of the two unbroken from U534, which was sank in 1945 and then salvaged in 1993: http://www.enigma.hoerenberg.com/index.php?cat=The%20U534%20messages&page=U534

A copy&paste quote from the project forums:

Today around 02:30 GMT+2 ThrasherX-17 from team Keep The Fire Alive! returned a plaintext of 76 letters long FNYG MXHU message:

leitungvvvuuustuetzpktxwwwhavenxxfffttteunszwozwovierhuermitvrrhhhvvvgeloest

The message says:
"AN LEITUNG VON U BOOT STUETZPUNKT WILHELMSHAVEN: FUNKTELEGRAMM EINS ZWO ZWO VIER HIER MIT RHV GELOEST"

Which translates to:

"To administration from U Boot Command (Headquater) Wilhelmshaven. Radio message 1224 solved with RHV (Hand Cipher System)"

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Fantastic news!