War in the age of terrorism

In the age of terrorism war has changed immensely. One of the main things being the increase in amount of terrorist attacks and the difficulty in determining civilian/tourists from terrorist. The U.S. welcomes people from all over the world and it is nearly impossible to determine if someone is a terrorist. Terrorist are becoming more intelligent and professional over time with new training and tactics. For example 9/11 and the twin towers, it must have took some extreme training and military intelligence in order to pull that off as professionally as they did. Another important issue is almost the same thing but in other countries. In the war on terror normal civilians in the country simply look normal to U.S. troops but there could be bombs strapped on them waiting to strike.  It is nearly impossible to determine weather or not a civilian could be a threat because who is going to expect a nice lady and her kid to have bombs strapped to them.