It is easy to get on the index, show one of the following:
Each kind of symbols that glorify or define down the nazi regime/time.
Excessive violence against human beings as end in itself.
Example: Once even Commando (C64) was banned coz you have killed humans after changing the human sprites into aliens it was officially sold
as Space Invasion.
There is indicated software like Doom which you can´t buy if
you are younger than 18.
And there is confiscated software (Wolfenstein 3d) which you can´t buy at all.
Eh, hope this is not too political.