Within the first few hours of launch, the Mac App Store has already been hacked although the hack is not yet available.
To hack the Mac App Store you'll simply need to install some software called Kickback that is being made available sometime in February this year.
We don't want to release kickback as soon as the [Mac App] Store gets released. I have a few reasons for that.
Most of the applications that go on the Mac App Store [in the first instance] will be decent, they'll be pretty good. Apple isn't going to put crap on the App Store as soon as it gets released. It'll probably take months for the App Store to actually have a bunch of crappy applications and when we feel that it has a lot of crap in it, we'll probably release Kickback.
So we're not going to release Kickback until well after the store's been established, well after developers have gotten their applications up. We don't want to devalue applications and frustrate developers.
Apple [AAPL] will more than likely not be able to patch this one up just yet as the hack hasn't been released just yet and the way it was hacked has also not been exposed. As quoted above, don't expect it quickly (perhaps February) as the hackers want time for the app store to develop a little.
Gizmodo point out that Apple should probably provide a better software demo system rather than Lite versions of apps so that users can decide if they want to keep the apps.