When hijacked jetliners crashed into New York's World Trade Center and the Pentagon on Sept. 11, 2001, the devastation brought terror to America's doorstep on an unprecedented scale. The attacks—which included another hijacked commercial airline flight that crashed in rural Pennsylvania—killed nearly 3,000 people and launched a global war on terrorism, spearheaded by the United States. The catastrophe also forever changed the way most Americans viewed their freedom and safety.

As the five-year anniversary of the Sept. 11 attacks nears, the global war on terror wages on in Afghanistan, Iraq and other Middle Eastern hotspots. But in addition to military missions to destroy terrorist groups abroad, the war on terrorism also hits close to home. Following Sept. 11, the federal government formed the Department of Homeland Security to coordinate the nation's security and disaster relief efforts and tasked the FBI to shift its focus to fighting terrorism. The federal government launched a color-coded warning system to gauge the current terrorist threat level. Fighter jets now routinely patrol the skies above major U.S. cities. And security checks at airports, border crossings and ports of entry have been re-engineered and bolstered with high-tech cameras and other devices to better screen for potential terrorism threats.

In response to the attacks, the government also created the TSA, short for Transportation Security Administration. The TSA oversees airport security and aims to prevent terrorist attacks through ramped-up passenger screening at airports, as well as screening of container ships in ports, trucks traveling the highways and commuter trains. Border security has also been heightened since 9/11, including the introduction of high-tech screening devices and biometric features to document visitors to the United States. The Department of Homeland Security's US-VISIT program is part of an effort to tighten border security by tracking foreign visitors' arrivals and departures from the United States. The program uses technology to capture a digital fingerprint and photograph of a visitor to authenticate their travel documents. Officials can cross-check a traveler's information with a database of known criminals and suspected terrorists. The Department of State also is rolling out updated passports, which include biometrics to help identify travelers and reduce fraud.

But the government's efforts to use technology to heighten security have encountered numerous hiccups. The American Civil Liberties Union, among other groups, has blasted the US-VISIT program for its collection of people's personal records and potential for racial profiling. Border screening efforts have also been criticized for being different at various ports of entry. Meanwhile, the FBI has faced an uphill battle to overhaul its antiquated computer systems and to better use technology to boost its terrorism-fighting capabilities.

The 9/11 attacks highlighted the need for not only the FBI, but for other local, state and federal agencies to work together to better collect and analyze stored personal data—at times mundane information like buying habits, Internet usage and credit card purchases—to possibly piece together patterns that could point to another terrorist plot in the making. Flight school records, airline ticket purchases and other activities of the Sept. 11 terrorists might not have seemed so random if there was a better system in place to connect the dots of their actions. Private data mining companies, which have primarily sold information about consumer's buying habits and other personal details to advertisers and marketers, have also started sifting through data for the federal government. The practice, however, has some civil liberties groups concerned that privacy is being overshadowed by the desire to keep tabs on potential terrorists at the risk of infringing on the rights of innocent people.

Nevertheless, this new emphasis on so-called data mining already has scored major victories. Case in point: In recent weeks, British authorities worked closely with U.S. intelligence and security officials to foil a potentially massive terrorist plot involving plans to blow up planes from the United Kingdom bound for the United States. The suspects were caught largely through widespread surveillance of their phone calls, Internet communications and travel activities. Donations for Pakistani earthquake relief were also tagged as a cover for financing the planned operation. Without large-scale surveillance and analysis of the suspects' online and offline activities, the potentially deadly plot might have slipped through the cracks and led to a disaster on a similar scale to 9/11.

But with methods like this, there is the inevitability that certain privacies and freedoms are curtailed. There is a fine line of balancing national security with the civil liberties of people who may be targeted in terrorist investigations. While government officials have been lauded for stopping potential attacks by hindering and nabbing would-be terrorists, President Bush has been criticized for using overly-aggressive search and surveillance techniques and detaining suspects at the expense of important civil rights. Recently, the Bush administration has come under fire for the disclosure of a controversial, domestic eavesdropping program by the National Security Agency involving the monitoring of e-mails and international phone calls.

Meanwhile, the USA Patriot Act, a sweeping piece of federal legislation passed in response to Sept. 11, gives law enforcement agencies more surveillance and investigative powers through warrants, wiretaps and other tools. The anti-terrorism law has been heavily criticized by civil liberties groups for violating people's privacy, freedom of speech and other constitutional rights and for lacking oversight from Congress and courts. The administration, however, has defended the law and its stepped-up anti-terrorism practices as necessary measures to stamp out terrorist activities and thwart another Sept. 11-style attack.