The findings released Wednesday by the Pew Research Center provide a gauge on how Web surfers have been responding to a computer bug nicknamed "Heartbleed" that affected more than 500,000 websites.
After word of the problem got out April 7, security specialists recommended Web surfers change their online passwords.
Thirty-nine percent of the 1,501 adults polled by Pew said they had changed their passwords or closed online accounts.
But 36 percent of the Internet users participating in the survey hadn't heard about Heartbleed at all.
The survey was taken from April 23 to April 27.