Mr. Laser Beam wrote:
HAL was told of the Monolith's true purpose (i.e. the big one at the end of the film) but was ordered to keep it secret from the rest of the crew - and that directly led to HAL's breakdown and murder of the crew.
Hal's system containing secured files, results in it killing five people, this (from 2010) never made any sense.
Computers commonly hold files that they don't allow open access to.