72 year law

I was looking on-line and saw the census bureau has a 72 year law where you can't get certain documents from the census before 72 years have gone by and I wanted to know more.
Can you explain to me what is the point of this law is and why did the law makers at the time in was  created thought they needed it.   I assume when they created it there must has been a reason to do it.
Can you please tell about the law and how it works and what it prevents.  I would also like to know do you have the legislation which made it a law and when it was created and signed by the US president.
Even through it passed there must be possible loop holes which could occur if someone could volid it.
I assume most of the data people get for the census is on the computer and the internet.
What kind of good census websites do you know of which you could share with me.
Anything you could share me and send would great.
Please do let me know
Stephen Hosmer