The number of Americans who say they've had important personal information stolen online – such as their social security number, credit card or bank account information -- is on the rise, according to a new Pew Research Center report.

In the survey, conducted in January, 18 percent of online adults said they have had personal information stolen. That's up from 11 percent in a July 2013 Pew survey. The report was released Monday.

The 50-64 age group reported the largest increase in stolen data, with 20 percent saying they had personal information stolen, up from 11 percent last year. The 18-29 age group reported the second largest increase, from 7 percent last year to 15 percent this year.

The number of adults who had an online account compromised or taken over without their permission — such as email or social media — remained flat at 21 percent.

The survey was done after news broke of Target Corp.'s massive pre-Christmas data breach, but well before last week's discovery of the "Heartbleed" bug, which has caused widespread worry across the Internet.

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The Target breach resulted in the theft of 40 million debit and credit card numbers, along with the personal information of up to 70 million people. The cost of replacing potentially stolen debit and credit cards has already reached into the tens of millions of dollars.

Other companies including Neiman Marcus and Michael's subsequently reported their own smaller data breaches.

It remains unclear whether hackers have been able to exploit Heartbleed, which went undetected for more than two years, to steal personal information. The bug is caused by a flaw in OpenSSL software, which is used on the Internet to provide security for both websites and networking devices such as routers, switchers and firewalls.

The Heartbleed bug is estimated to have affected 66 percent of active sites on the Internet, according to the Pew Research Center.

The Pew survey, conducted between Jan. 23 and 26, polled 1,002 adults living in the continental U.S. It has a margin of error of plus or minus 3.5 percentage points.

The Associated Press contributed to this report.