The Maemo 5 user interface is slightly different; the menu bar and info area are consolidated to the top of the display, and the four desktops can be customized with shortcuts and widgets.
At the Mobile World Congress in February 2010, it was announced that the Maemo project would be merging with Moblin to create the Mee Go mobile software platform.
Since Diablo (Maemo 4.1), Maemo supports "Seamless Software Update" (SSU), which allows incremental operating system upgrades "over the air" using the Advanced Packaging Tool, without the need for a full flash with every update.
The quick start guide for developers warns that Maemo security concentrates on preventing remote attacks (e.g. It also warns that Maemo's root account has a trivial default password (user: gainroot, password: rootme) which needs to be changed before enabling remote access.
Now, the XDA forums member Quixote78 made a tutorial how to restore original software on the TA-1000. Enter your Nokia 6 into Download mode connected with USB cable to your PC. After your device enter into Download mode, the button Edit Phone Information will be available. If you have any questions you can ask it in the comment section below, but I am sure you will be better off if you head to XDA forums and ask there, where the author of the tutorial could answer.