The study by the government, private and academic Internet security collaborative says only 42 percent of those surveyed have appropriate firewall protections to safeguard personal computers from hackers and other criminals. The finding contradicts the 80 percent of Americans who claim they have an adequate firewall installed, the NCSA reported.

The NCSA partnered with Norton security software developer Symantec for the study coinciding with the Department of Homeland Security's National Cyber Security Month in October. Officials say the polling firm Zogby conducted the survey of more than 3,000 Americans. The survey had a margin of error of plus or minus 1.6 percentage points.

The discrepancy in computers with adequate firewall protection and those who think they are protected was discovered after Symantec performed a checkup on 400 computers. The checkup had a margin of error of plus or minus 5 percentage points.

Despite the Internet security tools gap in claim vs. actual adequate protection, the study did find 95 percent of people surveyed have anti-virus software installed.

"Great strides have been made, but our citizens, economy and national infrastructure will remain at unnecessary risk until every computer user in America has anti-virus, anti-spyware and firewall software on their computers," NCSA Executive Director Michael Kaiser said in a statement.