callback
1.
A scheme used in {event-driven} programs where the program registers a {subroutine} (a "callback
handler") to handle a certain {event}. The program does not
call the handler directly but when the event occurs, the
{run-time system} calls the handler, usually passing it
arguments to describe the event.
2. A {user authentication} scheme used by some
computers running {dial-up} services. The user dials in to
the computer and gives his {user name} and {password}. The
computer then hangs up the connection and uses an {auto-dial}
{modem} to call back to the user's registered telephone
number. Thus, if an unauthorised person discovers a user's
password, the callback will go, not to him, but to the owner
of that login who will then know that his account is under
attack.
However, some {PABX}s can be fooled into thinking that the
caller has hung up by sending them a dial tone. When the
computer tries to call out on the same line it is not actually
dialing through to the authorised user but is still connected
to the original caller.
(1999-01-06)