To crack or fix a softwareto perform illegal actions
prohibited by the manafacturer. For example, adding a fix to a game can turn a trial version to a full version game without paying.
The person who programmes the fix can make the fix do anything, whether that is to repair your game or destroy it etc etc. People make illegal fix's to repair a games faults or errors, programmers can also make fix's enhance a games
graphics, volume controls, make it run without a cd etc etc.