  For a ringed space (X,O), we show that the deformations of the abelian
category Mod(O) of sheaves of O-modules are obtained from algebroid prestacks,
as introduced by Kontsevich. In case X is a quasi-compact separated scheme the
same is true for Qch(O), the category of quasi-coherent sheaves on X. It
follows in particular that there is a deformation equivalence between Mod(O)
and Qch(O).
