I've experienced this before, in my personal opinion its because of the download managers on the internet browsers that cause corrupt data when downloading large files over 1gb in size. For me it would happen alot with firefox and chrome, but eventually after setting it to re-download, and not using any other internet activity while its downloading, it managed to download fine.
I believe another thread was similar where the GM recommended using a download manager:
That should solve your integrity problems if its something to do with the browser's download managers if its related to corrupt data from lost packets ect..
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