RealNetworks Inc., owner of the Rhapsody online music service, dropped to its lowest value in 51/2 years in Nasdaq trading Wednesday after a judge extended a restraining order to ban the sale of its RealDVD software.

Piper Jaffray Cos. analyst Michael Olson cut his rating on the stock, saying Rhapsody hasn’t been able to crack the lead that Apple Inc.’s iTunes has in the online music market. A federal judge on Tuesday extended an order preventing RealNetworks from selling its DVD-copying program.