April 12 (UPI) -- More than half of Facebook users in the United States say they're very concerned about their personal data being sold, a new Gallup poll showed Thursday.
Respondents expressed concern after it emerged contractor Cambridge Analytica used a Facebook app to obtain information on as many as 87 million people without their knowledge.
Gallup's question about sold data topped a list of seven concerns. Fifty-five percent of U.S. Facebook users said they were "very concerned" about it.
"It's likely that Facebook users' concerns about their information being exploited by other companies are heightened after the recent Cambridge Analytica scandal, which prompted Zuckerberg's congressional testimony," Gallup analyst Justin McCarthy said in a statement.
Fifty-six percent said they have a Facebook page and 43 percent expressed concerns about possible invasion of privacy -- up from 30 percent in a similar 2011 survey.
Other concerns included Internet viruses -- which 36 percent deemed very concerning -- and unsolicited messages or ads appearing on their page.
Fifteen percent are very concerned about being shamed for things they say or do on Facebook, and 9 percent are very concerned about becoming upset or feeling bad about things they see others post. Thirteen percent voiced concern about spending too much time on Facebook.
The survey also asked Google users about the same issues. Fifty-seven percent said they're very concerned about personal information being sold and 44 percent about Google tracking their location history.
One in three Google users are very concerned about invasion of privacy and Internet viruses, and 36 percent are worried about Google sending them targeted ads based on browsing history.
More than 1,500 Americans participated in the survey, which had a margin of error of 4 points.