  We investigate the impact of f(R) modified gravity on the internal properties
of Milky Way sized dark matter halos in a set of cosmological zoom simulations
of seven halos from the Aquarius suite, carried out with our code MG-GADGET in
the Hu & Sawicki f(R) model. Also, we calculate the fifth forces in ideal
NFW-halos as well as in our cosmological simulations and compare them against
analytic model predictions for the fifth force inside spherical objects. We
find that these theoretical predictions match the forces in the ideal halos
very well, whereas their applicability is somewhat limited for realistic
cosmological halos. Our simulations show that f(R) gravity significantly
affects the dark matter density profile of Milky Way sized objects as well as
their circular velocities. In unscreened regions, the velocity dispersions are
increased by up to 40% with respect to LCDM for viable f(R) models. This
difference is larger than reported in previous works. The Solar circle is fully
screened in $f_{R0} = -10^{-6}$ models for Milky Way sized halos, while this
location is unscreened for slightly less massive objects. Within the scope of
our limited halo sample size, we do not find a clear dependence of the
concentration parameter of dark matter halos on $f_{R0}$.
