It can take less than 18 minutes to crack your phone's 4-digit PIN number.

Original story: On Monday, Google commercially launched a cloud-based mobile payments ecosystem that promises to let users pay for things with their Android smartphones.

In short, Google Wallet replaces the act of pulling out a wallet, handing over credit card, and signing your name with pulling out your smartphone, firing up an app, punching in a four-digit PIN number, and tapping your phone

But did you know it takes less than 18 minutes for a hacker, or even someone with a fancy calculator, to guess a four-digit numeric PIN? No matter what efforts Google and its partners have made to secure Google Wallet, PCMag's lead security analyst Neil Rubenking says the four-digit PIN authentication prevents him from trusting Google Wallet.

Rubenking referred me to some stats presented by Dino Dai Zovi (an independent security expert famous for hijacking a MacBook Pro) at the 2011 Black Hat Security Conference in August. According to Dai, if someone uses a brute-force attack, the method of simply going through different permutations of keys, it only takes:

1 8 minutes to crack a 4-digit numeric PIN

51 hours to crack a 4-digit alphanumeric PIN

8 years to crack a 6-digit alphanumeric PIN

2 million years to crack an 8-digit alphanumeric-complex PIN. Complex characters are any other symbols that aren't letters or digits.

Similarly, security expert Graham Cluley of Sophos Security was concerned whether or not users would choose sensible PINs.

In August, Sophos found that 67 percent of consumers don't use a password to protect their mobile phones. And if you do, please, Sophos begs of you, don't make it one of the 10 most common mobile PIN numbers, shown on the chart below.

For more on Google Wallet, check out PCMag's in a controlled environment in San Francisco, and the slideshow of at the end of this page.