  Minicharged particles (MCPs) arise naturally in extensions of the Standard
Model with hidden sector gauge groups. Many such extensions also contain
magnetic monopoles. For models containing both monopoles and MCPs, we clarify
the role of the Dirac charge quantization condition in restricting the possible
charges. We also show that monopoles of the hidden sector may manifest
themselves as MCPs, by a generalization of the Witten effect, which we call
"magnetic mixing".
