Originally Posted by
dj506
The answer in Chicago is "it depends." You don't say which airline you are flying from Chicago to Vienna. If it's a US based carrier, then you won't have to go through security again. You may just need to walk between terminals. Many times, if it's a foreign based airline (other than Lufthansa), you will need to take the train to Terminal 5. Then you will have to clear security there again.
+1
ORD can be tricky when connecting from an international flight to a domestic flight. I learned this lesson the hard way. I bought a snow gobe at NRT (Tokyo Airport), but had to mail it home because I had to clear security again to board my domestic flight.