When Rational® ClearCase® loads a file element into a snapshot view, it applies the file system's read-only attribute to the file. If you change this attribute, and modify the file without checking it out first, Rational ClearCase considers the file hijacked.
Only files under source control can be hijacked; view-private files are not under Rational ClearCase control and you can modify them without involving Rational ClearCase.
Hijacking takes a file outside of direct Rational ClearCase control. Although Rational ClearCase detects the change to the file, it is not a good practice.