If your cell phone were lost or stolen, you'd probably freak out, right?

Just think of all the sensitive personal information that's on your mobile device: contacts, passwords and PINS, maybe credit card or bank account numbers. And what about all of those personal pictures and texts—maybe a bit too personal, that are stored on that device. Would you want someone else to see them?

And yet, most people don't take even the basic steps to secure their mobile device. A new nationwide survey by Consumer Reports found that 34 percent of all smartphone owners do absolutely nothing, not even a simple code to lock the screen.

"This is one of the reasons why so many people's accounts get hacked when their mobile phone is lost or stolen," said security expert Robert Siciliano with BestIDTheftCompanys.com. "When the device is not password protected, anyone who finds or steals it has direct access to all of your accounts that automatically log-in as soon as an application is launched."

Consumer Reports found that only 36 percent of the smartphone users have set a 4-digit PIN to lock their phone.

Read MoreCell phone thefts soar as advocates hail 'kill switch'



"Four digits are better than nothing, but the strongest passcodes have at least eight digits in them and have a mix of letters, numbers and symbols," said Mike Gikas, a senior electronics editor at the magazine.

Even fewer people take more aggressive measures to protect the data on their phone, such as:

Install software that can find the phone if it's lost: 22 percent

Install an antivirus app: 14 percent

Use a PIN longer than 4 digits, a password or unlock pattern: 11 percent

Install software that can erase the data on the phone: 8 percent

Use security features other than screen lock, such as encryption: 7 percent

"I'm not surprised by these low numbers," said Timo Hirvonen, a senior researcher at the global security firm F-Secure. "Most people don't see the need for security on their mobile devices. This is very short-sighted considering the kinds of information people have on them and access with them."

The world is going mobile—and so are criminals. That smartphone you carry around with you all day long is now a lucrative target for cyber-thieves who want to gain access to your personal information.

Read MoreMobile addiction growing at an alarming rate



"That smartphone is a computer, like any other, and there's just as much risk of being a victim if you don't take the proper security precautions," said Alphonse Pascual, a senior analyst for security, risk and fraud at Javelin Strategy & Research. "Criminals are targeting those devices and people need to understand that."