Recently researches found at least two vulnerabilities of Google Wallet. The previous one requires the phone to be rooted and a brute force decryption of a file which is for hackers. The new one has none of those requirements, it is very easy and it is demonstrated in the video at the end of this post. It is very easy, the only thing you need to do is go into Google Wallet application settings menu and press the button to clear the data. The next time you will open the app it will ask you to set a new pin. After setting the new pin and adding the Google prepaid card you have full access to the funds. As you see, no rooting and no external app are used, just resetting the Google Wallet. Try not to loose your phone and be very careful to whom you giving it to as he requires only about 2 minutes to access Google Wallet.
Source: [The Smartphone Champ]