So if you choose to go, what precautions should you take?
Be Cautious on Public Transit: Rush hour on the trains might not be the best time to travel. If you can afford it, take taxis or private transport.
"Don't go where there is a lot of public. Don't be in the middle," Yeffet warns. "Don't be in the buses. Don' be in the trains. Don't be in an area that people know tourists go there."
Avoid Crowds: You can't avoid crowds when seeing the big sights of Europe. But think twice when you go to a site. Try not to cluster with other tourists.
Don't Wear Sneakers: This may seem a bit odd, but Diener points out that Europeans almost never wear sneakers outside of athletic activity. You don't want to stand out as a tourist, so don't lace up the sneakers.
Pick Your Hotel Wisely: Some big-name hotels are naturally targets more than some other places to sleep.
"Clearly, terrorists like to target highly visible large luxury hotels and public transit," Hobica said. "One could play it safe by staying in smaller boutique hotels or B&Bs, or hotels that aren't highly visible or famous."
That said, the larger hotels do offer larger security forces. Weigh your options.
Also, request a room on a low floor (but not the first floor) for an easier escape in case of fire or attack.
Register With the Embassy: "I'm headed to Germany later this week for a conference, and I plan to keep my plans but stay informed by registering with the U.S. State Department and local embassies, which can then better contact you in case of an emergency or send you any updates via e-mail," Banas said.
Have Emergency Numbers: Keep international roaming active on your cell phone and pre-program emergency numbers such as local consulates and travel providers.
The Folks Back Home: Leave detailed information about your whereabouts with people back home and plan to check in often.