In 2008, Konami filed a patent lawsuit against Harmonix (and MTV, and Viacom).
The suit alleged that Harmonix's Rock Band violates a pair of patents Konami obtained in 2002 and 2003, which relate to "simulated musical instruments, a music-game system and a musical-rhythm matching game".
Harmonix, which worked with Konami in 2003 to create Karaoke Revolution, developed Guitar Hero in 2005 — years after Konami had released its own guitar game GuitarFreaks in Japanese arcades. Likewise, Konami's DrumMania seemed to be echoed in Harmonix's Rock Band games.
That lawsuit has been settled. Both companies have agreed to dismiss "all claims and counterclaims" in the suit. According to Bloomberg, the terms of the settlement were not disclosed.