[AdelaideSimone]

I don't know how easy it is in Germany compared to the U S., but this is false. In the U.S., you absolute can sue (and it is extremely common) to force certain actions. See: constructive trust, mandatory injunction, prohibitive injunction, specific performance, recission, writ.

In all likelihood, you would not receive the source code in the U.S., though. If deadset against release, the outcome would likely be that the offender would be fined and injoined from any further distribution.