Digital fingerprinting has been much studied in the literature for more than 20 years, motivated by applications in copyright protection. A popular and practical approach is to use spread spectrum watermarking to embed fingerprints in multimedia objects. Solutions are normally only validated against known attacks in simulation. In this paper, we review known attacks on spread spectrum fingerprinting and give a mathematical argument for the efficacy of the so-called moderated minority extreme (MMX) attack. We also provide a new, mathematical description the obfuscation technique which we proposed at ICIP 2015, identifying some key properties which are necessary to resist the MMX and other attacks.