According to Consumer Reports' Annual State of the Net survey, 39 percent of the more than 100 million adult smartphone users in the U.S. don't implement even the most basic security measures, such as locking the screen, backing up data, or installing a locator app.

Consumer Reports says at least 7.1 million smartphones were irreparably damaged, lost, or stolen last year, but 69 percent of smartphone users hadn't backed up their data, and just 22 percent had installed software that would enable them to locate their phone.

The report also states that 5.6 million smartphone users experienced "undesired behavior" on their phones last year, such as the sending of unauthorized text messages or the accessing of accounts without permision, which indicates the presence of malware.

Consumer Reports advises users to take four basic precautions to secure their smartphones: use a strong passcode, install apps cautiously, be alert to insecure Wi-Fi, and turn off location tracking when it isn't needed.

"When you take your smart phone into your confidence, so to speak, you're also taking in a host of parties, including app developers, your wireless carrier and phone manufacturer, mobile advertisers, and the maker of your phone's operating system," Consumer Reports technology editor Jeff Fox said in a statement. "We recommend that all smart phone users take the basic precautions we outline in this report to ensure that their phones are secure from wireless threats."