The Heartbleed bug revealed a major lapse in the security of sensitive data on the Web, prompting broad warnings that Internet users should change many of their passwords and be on the lookout for scams.

But did the public notice?

To a large extent, yes, according to a study from the Pew Research Center's Internet and American Life Project released Wednesday.

The research group found that about 60 percent of American adults - and 64 percent of those online - were aware of the bug, which exposed millions of people's passwords and personal information. About 39 percent of Internet users surveyed took the extra steps of protecting their online accounts by either changing their passwords or canceling accounts, the study found.

"I think it's a pretty striking number," said Lee Rainie, the center's director.

Researchers had worried that after years of reports about security bugs and data breaches, the public would tune out the warnings.

The urgency of the coverage likely prompted people to act quickly to address the issue, Rainie said. "We didn't ask people how they'd heard about Heartbleed, but I'd guess that it was a combination of media coverage plus chatter in users' networks via social media and e-mail," he said. "And much of what we were seeing was the basic message, 'This one is really serious and you need to respond.' "

Still, there was room for improvement. The Heartbleed story didn't draw as much attention as other major news stories in the same cycle, the study found, indicating that people probably didn't fully understand what was happening.

Only 19 percent of those surveyed said they had heard "a lot" about the flaw, as compared with 46 percent who said the same of tensions between Russia and Ukraine. Overall, the Heartbleed story was about as big a news story as 2013 coverage of negotiations between the U.S. and Iran and the agreement to monitor Iran's nuclear program, the study said.

Despite the Heartbleed bug, many Americans feel their online information is "very" or "somewhat secure," according to the Pew report. And while 29 percent of Americans surveyed said that they think their information was put at risk as a result of Heartbleed, only 6 percent said they think the flaw actually allowed thieves to take their personal information.