It all comes down to whether you work in the industry or not, if you don't then that track stored on your computer is theft, if you have a recording contract, then it is a sample.
There was a long argument over how long a sample can be, now all IP, music, film, video, designs, etc, are all protected with ruthless efficiency, so if we want to find a legal limit on the length of a sample, let some programmers "sample" some microsoft code, then we will have our answer.
