The US should reopen most of the sites shut down after September 11 because of terrorism fears, a report says.
Security concerns led to the censorship of many official sites
The government-funded study found that the vast majority of official sites and databases posed little security risk.
In the aftermath of September 11, the US authorities shut down some 36 sites and more than 600 public databases.
But the report by the Rand Corporation concluded that details about potential targets like airports and power plants, was readily available elsewhere.
The September 11 attacks prompted a debate on access to information on the internet.
In the weeks that followed, the US Government, some organisations and some commercial sites removed or modified information on their websites for fear that the data might be used to launch other attacks.
Some of the information that disappeared from official US websites related to hazardous chemicals.
Other data removed related to information that could help enemies of the US identify targets and plan attacks, such as the location of military bases, pipelines and power plants.
The report, Mapping the Risks, by the Rand Corporation suggests that the censorship of the web in the months after September 11 was ill-advised.
The researchers looked at 5,000 federal web pages for the study. They found that none of the sites offered any information that was essential to a terrorist.
Some of the data taken offline was about airports
In any case, much of the data could be found in textbooks, non-government sites, trade journals or maps.
The same applied to virtually all of the 629 officials databases the researchers looked at.
In only four cases was there an argument to restrict prevent public access. These four databases had details about pipelines, nuclear reactors and dams.
The report appears to justify those who accused the Bush administration of acting rashly due to terrorist fears.
"It was a gigantic mistake, and I hope the study brings some rationality back to this policy," said Steven Aftergood, director of the Federation of American Scientists' project on government secrecy.
"Up to now, decisions have been made on a knee-jerk basis."