Boeing is using what it calls a "hard wall" in the software and has ensured no system settings can be changed in flight to stop an external input causing havoc.

See also this FAA report from last year:

Boeing's new 787 Dreamliner passenger jet may have a serious security vulnerability in its onboard computer networks that could allow passengers to access the plane's control systems, according to the U.S. Federal Aviation Administration.

The computer network in the Dreamliner's passenger compartment, designed to give passengers in-flight internet access, is connected to the plane's control, navigation and communication systems, an FAA report reveals.

One gets the impression that the "Hard Wall" could also be referred to as a "Band Aid."

RE: Hackers hardwalled from 787