In response, federal, state and local law enforcement agencies across the country went to a heightened state of alert, security officers worked overtime guarding critical infrastructure sites and the department of homeland security (DHS) urged the general public to be extra vigilant while going about their daily routines.
Since September 11 2001 there have been no major acts of terrorism in the United States.
Proponents of the colour-coded alert system say it provides a "deterrent" effect, discouraging terrorist groups from following through on planned attacks by publicly communicating that the government has intelligence on potential threats.
Critics, however, say the programme does little to enhance national security and drains valuable resources from state and local economies. They also caution that the multiple code-orange alerts may actually be numbing the public to the ongoing threat of domestic terrorism, creating a "warning fatigue" syndrome.
The US Congress is currently reviewing the system, with scrutiny coming from both Democrats and Republicans alike.
"It's my judgment that the colour-coded system should be eliminated. While the system may have served some initial purpose, I don't believe that the colour codes are serving us well today," said member of Congress Jim Turner, a Democrat from Texas, at a recent hearing conducted by the select committee on homeland security.
Whether the heightened alerts are preventing terrorist attacks is the key question in Washington. Some experts, sceptical of certain aspects of the system, said they remained confident that the five previous code orange announcements gave pause to terrorist cells who may have been preparing large-scale attacks on US targets.
"I think it's quite likely that we are disrupting plans that are in process," said David Heyman, director of the homeland security programme at the Centre for Strategic International Studies, a Washington think-tank.
After the most recent code orange alert issued on 21 December last year, Secretary of Homeland Security Tom Ridge said the system had proved effective as a deterrence mechanism.
Attacks on hold
Police inspect a car in December
last year during code orange
"We know from experience that the increased security we implement when we raise the threat level, along with increased vigilance, can help disrupt or deter terrorist attacks," Ridge said.
Randall Larson, a homeland defence expert, said terrorists would likely put attacks on hold during an elevated threat warning, and then stage them at a later time.
"I think it would perhaps be more likely that it would delay it," Larson said. "I [speaking of terrorists] might delay what I was doing, but I wouldn't necessarily not do it."
Larson said terrorist groups would likely wait for a lower threat level before striking again.
"Probably the next large terrorist attack is going to happen when we're at yellow [high threat level]," he said. "If I were a terrorist and was planning an attack and then all of a sudden I heard on television they were planning for an attack, I might wait a month."
The homeland security department based the latest code orange alert on intelligence that suggested terrorist groups might have been planning to hijack airplanes to use in 9/11-style attacks on US targets, DHS officials said at the time.
Still, the five orange alerts issued thus far were vague in nature and provided little specific information, something that has lawmakers in Washington concerned that both the public and local law enforcement agencies might let their guard down prematurely.
"Responding aimlessly to a generalised warning draws down resources without any assurance of enhancing safety"
chairman of the select committee on homeland security
"Responding aimlessly over and over to a generalised warning draws down resources without any assurance of enhancing anyone's safety," said Christopher Cox, chairman of the select committee on homeland security. "It may, over time, actually contribute to a degradation of this nation's vigilance - warning fatigue - and so diminish the utility of the homeland security advisory system."
Cox and other members of Congress, Republican and Democrat, urged the DHS to develop a system designed to deliver more specific warnings based on regional and local threat information.
Testifying recently at the House homeland security hearing, Admiral James Loy, deputy secretary of homeland security, said the colour-coded system was part of an "evolution" in US national security strategy and that the flexibility of the programme was greatly improved.
"I believe we have reached a threshold in that evolution where the [advisory alert] system serves the nation well," Loy said.
Loy said the most recent alert, aimed more directly at the aviation industry, demonstrated that the DHS had improved its ability to issue more sector-specific warnings.
Aside from questions over the alert system's effectiveness, are concerns about its costs to states and local communities, many of whom are still suffering from anaemic economies.
"To a certain extent, our government overreactions could cause more damage to the economy than the terrorists ever could," Larson said.
Heyman estimated it costs the country $1 billion per week during an elevated threat level. Not only must states and cities purchase costly new equipment and pay large amounts of overtime, their economies lose millions of dollars in revenue from a decrease in travel during heightened alerts, he said. Cox cited reports that said New York City has spent roughly $5 million per week on code orange-related expenses.
George Bush addresses the
Conference of Mayors
The US Conference of Mayors released a report in January saying that 76% of 168 cities surveyed had not received any money from the $1.5 billion Congress appropriated in 2003 for first responders and the protection of critical infrastructure.
Without adequate federal funding, state and local governments will be "cutting across the board" to pay for the costs of the code orange alerts, Heyman said.
However, he also said most of the new equipment needed for security alerts had already been purchased, meaning future alerts would likely be less expensive.
"A lot of what we're paying for right now is to build the system," he said.
Even critics of the colour-coded system acknowledged the difficult position the Bush administration is in politically because of the ongoing terrorist threat. If it issues non-specific threat warnings followed by no attacks, it leaves itself open to criticism from citizens who say the colour codes create costs and inconveniences without really telling communities how to protect themselves. On the other hand, if no such warnings were issued and a major attack took place, the anti-government backlash would be deafening, experts said.
"I think they're doing a pretty good job with what they have," Larson said of the no-win situation.
Still, he said the administration is probably playing a bit of politics by trying to cover itself against any potential accusations that it failed to warn the American public of an impending attack.
"As we get into an election year, [the Bush administration] are going to be, 'Well we don't want to get caught by surprise,'" he said.