If a message like "It may have been corrupted or tampered with during downloading” occurs when trying to install older versions of Mac OS X, it might be that the installer is too old and the certificate has expired.
To fix this, set the date and time the install is being done to some time a few years in the past (about the time the installer would have been current). Set it using the date command from terminal: date {month}{day}{hour}{minute}{year} (example date 010101002015 for 1 am on 1 Jan 2015) then install again.
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