Read his book. He talks all about it. Hawking later corrected himself as other scientists jumped on Susskind's bandwagon [They even had a couple of cute bets arranged (for $1 and another for a baseball encyclopedia)].
Hawking claimed that information is lost forever upon entry into a black hole. Susskind argued that information cannot be destroyed, it must be conserved, otherwise all physical laws are in danger. Eventually, Hawking conceded and thus arose the idea of Hawking Radiation. It balanced the problem of information loss.
Basically, information in the tiniest meaningful quantity is on the Planck scale. All "information" of matter can be broken down into these Planck-sized bits. Susskind showed that particles entering black holes encounter a strange world where 2 different outcomes become reality. One outcome is that the particle is destroyed forever. However, for observers outside the black hole, another equally true state of reality is that the particle becomes evenly dispersed across the surface area of the black hole in broken planck-sized bits. One "reality" is destruction, the "other reality" is the surface area of the black hole expanding with the addition of each particle. Both realities for one particle are true and exist simultaneously. It's weird, but his book explains it a lot better than I can.
