It's "whoever prepares for the commission of a [hacking] offence by acquiring computer programs for the commission of the offence" and it's been interpreted that downloading nmap can be preparing for an offence, therefore punishable. Giving copies to others (e.g. running a Debian mirror) is also likely illegal, but I doubt anyone's been charged for that yet.

https://www.gesetze-im-internet.de/englisch_stgb/englisch_st...