Dynamic Tardos Traitor Tracing Schemes
  We construct binary dynamic traitor tracing schemes, where the number of watermark bits needed to trace and disconnect any coalition of pirates is quadratic in the number of pirates, and logarithmic in the total number of users and the error probability. Our results improve upon results of Tassa, and our schemes have several other advantages, such as being able to generate all codewords in advance, a simple accusation method, and flexibility when the feedback from the pirate network is delayed. 
Thijs Laarhoven, Jeroen Doumen, Peter Roelse, Boris Skoric, Benne de   Weger
cs.CR