so I'm trying to install either Mavericks or Yosemite on this MBP. But I keep on getting a message that says "my copy of the installer is corrupt or may have been tampered with during downloading". I'm trying to install the OS via a USB stick that was created using the "createmedia" command. Using this page https://github.com/notpeter/apple-installer-checksums - I found out my Mavericks installer is most likely corrupt - My Yosemite installer checks out fine I highly doubt the problem is the USB stick since I've recently used it to install Windows 10. Any ideas? Thanks update: just tried El Capitan and no issues installing it. the SHA1 for El Capital checks out fine.