cases in which checksum doesn't work
I've written a program that calculates checkSum to a given file.

Can you please give me a case when the checkSum says everything's ok with a file, when there's actually a data flaw? 
    
Thanks
cases in which checksum doesn't work
===

I've written a program that calculates checkSum to a given file.

Can you please give me a case when the checkSum says everything's ok with a file, when there's actually a data flaw? 
    
Thanks