The best source I've found so far is the Reuters article FACTBOX: Rise and fall of the SocGen rogue trader. It outlines the fraud thus:
* The alleged fraud, as outlined by the bank, included a genuine long position in regulated stock market index futures, contracts bought in the hope that prices would rise.
* Usually an arbitrageur hedges such a long position with an equal and opposite sale, or short position, reaping a profit from any gaps between the values of the two transactions.
* The SocGen trader did hedge the first position with a second, but the trades in that portfolio were fake. So the bank was unwittingly holding long futures positions without cover, leaving it exposed to the risk that prices would fall.
* To evade controls, for the second portfolio he chose unregulated over-the-counter derivatives which do not need a downpayment, including forward contracts.
* Because there was no downpayment, or margin, these trades were not subject to the same immediate checks as the real futures positions held in the first portfolio.
* Since the real and fake trades balanced each other out, SocGen says its computers perceived "low residual risk" overall.
* As the market turned against him, he sought to cover up mounting losses to avoid further tiers of compliance checks.
The only "computer" angle (besides tricking the controls which measure risk) involved the following:
* The bank alleges that he misappropriated computer passwords and faked documents.
"Misappropriating computer passwords" could be accomplished by using shared accounts, accounts on sticky notes, or any of the other poor practices used in group settings.
Lending credence to the computer angle is this Wall Street Journal story:
According to Mr. Bouton, the Société Générale chairman, Mr. Kerviel began conducting fraudulent trades sometime in 2007. People familiar with Mr. Kerviel's behavior believe he worked late into the night, essentially burrowing into Société Générale's computers, as he allegedly built a multilayered way to hide his trades by hacking into the computer systems.
Société Générale's computer systems are considered some of the most complex in banking for handling equity derivatives, that is, investment contracts whose value moves with the value of other assets. Officials of the bank believe Mr. Kerviel spent many hours of hacking to eliminate controls that would have blocked his super-sized bets. Changes he is said to have made enabled him to eliminate credit and trade-size controls, so the bank's risk managers couldn't see his giant trades on the direction of indexes.
If we focus on what Kerviel is alleged to have done, rather than how it is described, it's possible the "elimination of controls" via "changes" could be considered "hacking."
Let's see what happens! The only good aspect of this intrusion is that the investigation report should be public, because the offender is going to be prosecuted.