Frezell's computer has the code to open Penn's door, not his computer password.
The Auto Unlocking Device is not available to anyone who didn't get access to that from their pre-order.
I read on the Eidos forums that someone looked in the game text, and discovered no mention of Penn's password, meaning that it isn't on any of the data secretary pads in the game. He speculated that it must be written somewhere.
Since people HAVE discovered the password, I'd really LOVE to know how. Was it leaked by one of the developers? It seems very suspicious that NOWHERE has anyone mentioned where the password is found. A lot of people have said what it IS, but not where. And yes, I saw the "it's behind a bookshelf" but I think that's a load of bull. Someone made that up and it's just been passed around like a rumor. No post ever says WHICH bookshelf.
I think the designers just either forgot or decided not to have this quest doable without upgraded hacking. It is a side quest, after all. And others have remarked that other side quests also cannot be completed without upgrading hacking.
Still, I'd love to know how people found out what the password WAS to begin with.