What was the decree which forced us to light the Chanuka lights inside?
Rashi said it was the Chabarim who banned all light outside of their temple. So they wouldn't find the Chanuka lights, we moved then inside.
The Bach argues, saying that such a decree wouldn't be considered Shmad (since it also affected non-Jews*), and hiding it inside the house wouldn't have saved the Jews anyways, as the Chabarim also did house inspections.
Rather, he writes (671:8) that there was a general decree against the Jewish religion.
As such, we would have to give up our life rather them give up Chanuka lights, so we had to continue lighting them. However, as the Mitzvah is fulfilled inside just as well as outside, there is no harm moving the menora inside.
*this could also teach the geder of Shmad, why the Soviet Union may have not fit into the category of Gezeras Shmad, why the Frierdiker Rebbe did not have to have mesirus nefesh, but did anyways