A would-be bomber (perhaps suicide, perhaps not) was stopped at the United States embassy in Vienna when his backpack full of explosives and nails set off the metal detector, and he panicked and ran.
Investigation is under way right now to determine if his backpack was actually a viable explosive. I'd put even odds on it not being viable -- a bomber who doesn't realize they're going to set of the metal detector, and who then leaves (instead of rushing the facility and detonating the device) may not be entirely there. Apparently, he has yet to give any kind of coherent statement, either.
The would-be bomber is a Bosnian national.