USB “installer corrupted” error

I went to upgrade an old iMac to Yosemite with my trusty USB stick, only to get this message: 

“This copy of the Install OS X [OS X Name] application can’t be verified. It may have been corrupted or tampered with during downloading.”

Found the solution here:

Quote: Due to an expiration of OS X App Store certificates, installers of OS X downloaded prior to February 14th of 2016  can’t be used to re-install OS X without encoutering this error.

Solution: While still booted from the installer, go to the Utilities menu and open Terminal and and type:

date 1010101015

This will set the date and time to the 10th of October 2015 at 10:10 (it’s just easy to remember, but any date in the five last years or so should work). Then exit Terminal and proceed with the installation/upgrade.