Security experts have been concerned for days about an attack similar to the one in Mumbai, India, which left 166 people dead. The State Department said Monday the alert is focused on Europe - not the U.S. - and that the decision to issue the alert to travelers was based on a cumulative analysis over a lengthy period of time and not something that just popped up over the weekend.
In the mountains of Northwest Pakistan, eight militants of German nationality were killed in a suspected U.S. drone strike, an event most probably linked to intelligence behind the new alert.
Like previous travel alerts, this one is short on specifics.
"We need to be careful- that's like common sense. But they need to be, like, more specific- careful of what? Like, do you know something you want us to know?" Mustafa Basri, DePaul student, said
What the intelligence community knows is that there has been increased "chatter" in terrorist circles, and part of this alert is based on information from a German citizen of Afghan origin who was arrested this summer after taking weapons training in Pakistan.
"This is the kind of warning I actually an encouraged by because it's focused. It doesn't say all of Europe. It tends to say France and Germany in particular, and the French and Germans have said the same thing. It doesn't say don't go. It says take reasonable precautions," said Prof. Thomas Mockaitis, DePaul University.
Mockaitis is a history professor and expert on terrorism issues who suggests that the threat since 9-11 has shifted from attacking symbols and landmarks to commando-style raids - like the 2008 attacks in Mumbai - simpler to execute but still capable of exacting a human toll while creating great fear.
"Be cautious and be aware that we are following, you know, multiple streams of threat information and we felt having, you know, tracked intelligence over a lengthy period of time, it was appropriate to issue this alert at this moment," said PJ Crowley, U.S. State Dept.
"Be aware of what's going on, don't be traveling with your iPods on, make sure you know what's around you, but still go and enjoy yourself in Europe," said Allie Liberacki, DePaul student.
That is, in fact, the government message: be mindful of places and events that will draw large crowds- airports, mass transit, big hotels and restaurants.
"I'm going to Europe next week. I'm not the least bit concerned about going. I think if you take yourself hostage to these kind of fears, you end up giving the terrorist what they want," said another man.
The state department is recommending travelers abroad register their whereabouts and plans with the U.S. Embassy in their country of destination, which can be done online. On Sunday, there were more than 8,000 new registrations worldwide, which is three times the typical number.