>> However, one might also conjecture that the probability of any two 
>> arbitrary messages having the same [MD5] hash code would be 2^(-128).
>
> Random fact:
>
> 2^(-128) ~= 2.93 * 10^(-39)
>
> Winning the National Lottery (assuming you only bought 1 ticket) has a 
> probability of roughly 7.15 * 10^(-8).
>
> If my arithmetic is right, that means that winning the National Lottery 
> jackpot 5 times back-to-back is still more than 637 times *more* likely 
> than something with a probability of 2^(-128) happening.
>
> Assuming the probability of a random file mutation leaving the MD5 hash 
> unchanged really *is* 2^(-128), it's a pretty unlikely event. You should 
> probably worry more about the building being burned to the ground...

If you are only worried about one file per week and you don't backup off 
site, then sure...

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