Welcome to the MultiBit forum.
Please use this forum for any questions you have about MultiBit.
MultiBit is a thin client that only downloads headers instead of the full block chain. It uses the library called bitcoinj. You can find out more about the security of different types of clients at the 'Thin Client Security' wiki entry.
The main MultiBit website where you can download the application is:
https://multibit.org
If you spot a bug that doesn't really need any discussion, it is a bit easier for me if you post it directly into the github issue tracker.
Thanks.
Jim