  We introduce and study the problem of scrambler hacking, which is the
procedure of quantum information extraction from and installation on a quantum
scrambler given only partial access. This problem necessarily emerges from a
central topic in contemporary physics - information recovery from systems
undergoing scrambling dynamics, such as the Hayden-Preskill protocol in black
hole studies - because one must replace quantum data with another when
extracting it due to the no-cloning theorem. For large scramblers, we supply
analytical formulas for the optimal hacking fidelity, a quantitative measure of
the effectiveness of scrambler hacking with limited access. In the two-user
scenario where Bob attempts to hack Alice's data, we find that the optimal
fidelity converges to $64/(9\pi^2)\approx0.72$ with increasing Bob's hacking
space relative to Alice's user space. We applied our results to the black hole
information problem and showed that the limited hacking fidelity implies the
reflectivity decay of a black hole as an information mirror, which questions
the solvability of the black hole information paradox through the
Hayden-Preskill type protocol.
