"The government refuses to confirm or deny whether someone is on the list, officially called the Terrorist Screening Database, or divulge the criteria used to make the decisions—other than to say the database includes 'individuals known or suspected to be or have been engaged in conduct constituting, in preparation for, in aid of, or related to terrorism and terrorist activities.' Even less is known about the secondary watch lists that are derived from the main one."
Governments wade into treacherous waters when they compile lists of people who might cause their countries harm. As fears about Japanese-Americans and Communists have demonstrated in the past, predictions about individual behavior are often inaccurate, the motivations for list-making aren't always noble and concerns about threats are frequently overblown.
So it might seem that current efforts to identify and track potential terrorists would be approached with caution. Yet the federal government's main terrorist watch list has grown to at least 700,000 people, with little scrutiny over how the determinations are made or the impact on those marked with the terrorist label.