This paper points out an interesting weakness in PRNG's, but the real threat to BTC with respect to PRNG's may be far more serious: Bruce Schneier has long written that the probability is unacceptably high that the NSA has installed a PRNG backdoor in the widely accepted SHA-3 standard protocol for cryptography (which NIST grudgingly accepted only with a footnoted caveat that one might prefer to use a more efficient alternative).  If such a backdoor exists (which seems nearly certain to me), the NSA can rather easily crack into any level it chooses of such encryption, and that means virtually all the BTC protocols - which would be the rather instant death of such cryptocurrencies.  Is Quarkcoin the only alternative cryptocoin that does not use the tainted PNRG?