blockchain.info is the official wallet and main blockchain used for bitcoin. It is indeed trusted. It is also usable for games like this that send coins back to your sending address since it gives you one address for sending and receiving. Most all other web wallets do not allow this. Exchange sites DEFINITELY don't allow it.
Use client based wallets like Multibit and Electrum instead.
Where do you get official from?
Blockchain.info offers a JavaScript based client, using it's service to do the data/storage. Assuming the design does not change and the JavaScript they host is not tampered with, by either internal or external sources, it offers a secure platform.
Your digital wallet is encrypted using the password you supply and is not accessible by Blockchain.info. The wallet is only accessible inside the browser instance running on your computer, though a FireFox plugin could target blockchain.info wallets.
If you forget your password your data becomes inaccessible by anyone. Whereas with other services they host a digital wallet and have complete access to make any changes at any time. Even more troubling is that every user shares the same wallet opening up users to another M.T. Gox indecent.