The original installation media for Mac OS X Snow Leopard was a 10.6 DVD. The DVD was only updated once to version 10.6.3. In order to provide more frequent updates to users, Apple is now slipstreaming the latest version of OS X directly into the download. Upon fresh installation, no updating is necessary!
If you purchased Mountain Lion from the App Store prior to September 19, 2012, you most likely have 10.8.0 or 10.8.1. To re-download Mountain Lion and update your App to 10.8.2, simply log into the Mac App Store and click Update. When the download finishes, the app will automatically open. The updated 10.8.2 Install Mac OS X Mountain Lion App can be found in the Applications folder. You can then re-create your UniBeast installation USB.
If you don't see the Update button, follow this simple procedure.
1. Delete your existing copy of Install Mac OS X Mountain Lion.app from Applications folder.
2. Hold down the alt/option key on your keyboard, and click the App Store icon.
3. With alt/option key held, click on Purchased
4. With alt/option key held, click on OS X Mountain Lion
5. With alt/option key held, click on Install
If neither of the above processes work for you, try creating a new User account. You can delete it later.
1. Open System Preferences
2. Click on Accounts
3. Click Lock Icon
4. Click (+) to add a new User
5. Create a new Admin User
6. Log out, and log into new User
7. Proceed with steps above.
OS X 10.8.2 Update
Mac OS X 10.7.5 Update
UniBeast: Install Mac OS X Lion Using an All-In-One Bootable USB Drive