What does proper attribution means ?

I was going through some instructions for March Cook-Off 2014 , it is written there " If anyone is using code from some other source in his submission, he should provide proper proper attribution. Failing this, it may be considered plagiarism and the submission will be subject to disqualification." so what kind of codes needs attribution during my 4 months of using codechef i heven’t seen any one putting up an attribution in his code ! for eg i sometimes use code-snippets directly from books and from my past code directory on my puter , should i worry about that ?

Just make a comment in the code about the source. I’d put author’s name and source site there. It should also be publicly available, I guess - in order to prevent elaborate cheating.

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