A certain pseudo-random number generator (PRNG) algorithm that uses XOR and 3-bit random hops (aka "Algorithm X3"), as used in OpenBSD 2.8 through 4.2, allows remote attackers to guess sensitive values such as DNS transaction IDs by observing a sequence of previously generated values.  NOTE: this issue can be leveraged for attacks such as DNS cache poisoning against OpenBSD's modification of BIND.