It is tempting to overreact to warnings that al-Qaeda is preparing an attack on a large financial center in Asia. That would be a mistake. If accurate a big if the reports should spur officials to better prepare for that awful possibility. But the news is not really new: Japan has already suffered one terrorist attack and officials here have long been aware that the country is a target of Islamic extremists. These reports are a reminder of the new security environment in which we now live and a call for vigilance, but they must not be allowed to dominate the lives of ordinary citizens. If that happens it would signify a victory for the terrorists.

Senior French terrorism investigator Jean-Louis Bruguiere warned in an interview last week in the Financial Times that al-Qaeda was planning to attack financial centers in Asia to undermine confidence in the region and undermine economic growth. The list of possible targets includes Tokyo, Sydney and Singapore. According to Mr. Bruguiere, there are “several elements of information that make us think that countries in this region, especially Japan, could have been targeted.”

The warning is appropriate, even if the information is not very specific. The governments of Japan, Singapore and Australia have said that they are unaware of any specific threat. Mr. Bruguiere said that he is ringing the alarm because “There is not enough public consciousness of the terrorist risk. There is more work to be done to sensitize the public to the threat.”

That is odd, if it is true, as the region should be well aware of the danger. Terrorism is no stranger to Southeast Asia: There has been a series of terrible attacks in Indonesia, Thailand is experiencing an Islamic insurgency in its southern provinces, the Philippines have long battled Islamic separatists, and Islamic groups have been identified and cells broken in Singapore and Malaysia. A terrorist has been convicted of plotting attacks in Australia. China battles its own Islamic separatists.

Japan should be alert, too. As a U.S. ally with a military presence in Iraq, it is an obvious target, as were Spain and Britain. Al-Qaeda has, in fact, threatened to attack Japanese targets for Tokyo’s support of the United States. Alleged al-Qaeda activists have been identified as being in the country. More significantly, however, Japan has already experienced a terrorist attack: The 1995 sarin gas attack by the Aum Shinrikyo religious group, which killed 12 people and injured hundreds more, underscored the danger posed by terrorists and made plain Japanese vulnerabilities.

Tokyo says that it is “alert” to the prospect of terrorist attacks, noting that the information provided by Mr. Bruguiere is not very concrete. It is continuing its antiterrorism cooperation with other governments around the world.

A response should occur on two levels. First and foremost, every effort must be made to prevent such attacks. Japan has been hampered in this endeavor by a division of labor among its intelligence agencies that could prevent valuable information from getting to security officials in time. The government will release a report next month that details ways to strengthen intelligence operations. Surveillance has been increased at public-transport facilities, but its effectiveness is challenged by the sheer volume of passengers.

The continuing debate over how best to balance privacy with the need for greater safety is another factor: Their respective weights are changing, but it is important to remember that terrorists are fighting against that very freedom. To greatly restrict personal liberties in the name of greater security would hand the terrorists a victory.

The London Metropolitan’s planned response to a terrorist assault greatly facilitated its response to the July bombings. The Japanese government must be better prepared for a terrorist attack. First responders must be ready, equipment available and evacuation procedures prepared. Health-care facilities must be stocked for a variety of contingencies and personnel properly trained. Plans must be coordinated among various local and national government agencies. Significantly, the public must be confident that the government is ready so that there will be no panic.

Even if Mr. Bruguiere’s warning proves to be premature or unfounded, the odds of a terrorist attack on Japan are increasing. Technology is putting ever more powerful devices in the hands of individuals. Governments must be ready for this new environment. Citizens have a role to play as well. They must assist their governments in preparing for acts of terrorism and in keeping an eye out for suspicious behavior. At the same time, they should continue to lead their normal lives and not overreact to threats of terrorism. To give in to fear is to give the terrorists the victory they seek.

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