The UWG (Gesetz gegen den unlauteren Wettbewerb, The German Act against Unfair Competition) prohibits certain trade practices, which are considered unfair and codifies an obligation to issue a warning (called Abmahnung) to the offender before going to court. The case is settled (if it is) by giving the alleged offender notice of the conduct regarded as violating the Act and is called upon to sign a cease and desist declaration, containing a contractual penalty clause.
The big picture here is that according to the OLG Hamburg the omission of privacy related information (§ 13 Abs.1 TMG) may indeed be a violation of the UWG and therefore companies could find themselves dragged in front of courts by their competitors.
All the more reasons to get your Datenschutzerklärung in order.
Via Delegedata [German]