BBC News Online's Kevin Anderson in Washington

During World War II, soldiers and sailors were admonished that loose lips sink ships, but in the age of the internet some are wondering whether loose links pose more of a problem.

The attacks on 11 September have renewed a debate on access to information on the internet.

The US Government, some organisations and some commercial sites are removing or modifying information on their websites for fear that the information might be used to launch other attacks.

Being 'responsible citizens'

The Federation of American Scientists' (FAS) website has a wealth of information on the US military and intelligence.

Steven Aftergood, a senior research analyst who concentrates on government secrecy and intelligence said since 11 September, FAS removed or modified a number of pages from its site including the locations and layout of intelligence facilities and some detailed information about nuclear weapons facilities abroad.

FAS has published many documents the US military would rather have kept out of the public eye

"We are just trying to be responsible citizens. September 11 was an earthquake in national security policy," he said.

The attacks again raised the issue of the balance between civil liberties and security in an open, democratic society, and 11 September has radically changed the debate.

"The balance has necessarily shifted. If there are people among us who are intent on committing spectacular mass murders, then obviously our conduct of public life has to be adjusted accordingly in order to protect civil liberties," he said.

"Much of my work has been oriented towards resisting the possibility of government overreaching and official abuse of power, but that hypothetical threat pales to what has actually taken place."

Difficult debates

The attacks have caused many organisations to go through a wrenching debate as they re-evaluate what should be publicly available on the internet.

OMB Watch provides easy access to several publicly available government databases with a focus on environmental issues.

Their sites allow users to enter their postal codes and find out about chemical plants and toxic chemical releases in their areas, but some fear that the information could be used by terrorists.

In the face of criticism, OMB Watch decided to leave environmental databases online

OMB Watch Executive Director Gary Bass said in a statement: "I was surprised in the wake of the September 11 terrorist attacks to receive hostile e-mail. One individual wondered 'how much blood will be on your hands for posting' information about environmental dangers."

After much internal discussion about the responsibility of publishing the information on the internet, they decided that it would be irresponsible to take down the databases, Mr Bass said.

"The information may not only aid and abet terrorists, as we have been accused of, but it also lets workers and people protect themselves from dangers in their communities," he said.

Government offline

OMB Watch has also been tracking the amount of information that government websites have removed in the wake of the attacks.

• The Environmental Protection Agency has removed Risk Management Plans from their website. The plans provide information about the dangers of chemical accidents and how to prevent them, according to OMB Watch.
• The Department of Transportation "has discontinued providing open access to the National Pipeline Mapping System (NPMS). Recent events have focused additional security concerns on critical infrastructure systems," according to its website.
• The Agency for Toxic Substances and Disease Registry has removed a report from its website on chemical site security.
• The National Imagery and Mapping Agency has suspended all sales of maps of military installations as well as its most detailed maps of other US locations.

Several other government agencies including the Federal Aviation Administration, the Bureau of Transportation Statistics, the Internal Revenue Service and the Nuclear Regulatory Commission (NRC) have also removed information from their sites.

Like many government agencies, the NRC is reviewing the information on its website, said spokeswoman Rosetta Virgilio.

"We have a team of folks looking at it, looking at information that terrorists might be interested in," she said.

Site shuttered

But some sites have been the first casualties of the new war on terrorism.

Travis Towle remembers watching a news report about the possibility that the government might seize the assets of some internet companies with links to terrorism.

Mr Towle operates a streaming media company in Topeka Kansas, and his company hosted a site called IRA Radio.com, "a web site which is for Irish news & media coverage with regard to the ongoing British presence in the occupied six counties of Ireland with a view toward correcting misrepresentations."

IRA Radio.com shut down rather than face a costly legal battle

The morning after seeing the news report, he received a call from his internet service providers.

They were concerned that their assets might be seized, and they did not want to be a test case, Mr Towle said.

After speaking with the advisory board of his company, he decided to take down the site.

"Everybody has a right to free speech, but the problem comes down to cash," he said.

Their attorneys said it would take up to $500,000 to argue the case, and the fledgling company did not want to risk the five years of work they had spent building it into a viable business.

In three months, they will reassess the situation, and they hope to quietly relaunch the site.