  Based on the analysis of $6$-digit one-time passwords(OTP) generated by
DIGIPASS GO3 we were able to reconstruct the synchronisation system of the
token, the OTP generating algorithm and the verification protocol in details
essential for an attack. The OTPs are more predictable than expected. A forgery
attack is described. We argue the attack success probability is $8^{-5}$. That
is much higher than $10^{-6}$ which may be expected if all the digits are
independent and uniformly distributed. Under natural assumptions even in a
relatively small bank or company with $10^4$ customers the number of
compromised accounts during a year may be more than $100$.

Cryptography and Security