I bought a macbook pro off craigslist awhile back that the guy couldn't load a OS to. It came with a 160GB regular platter hd, but said nothing was on it. I had a hard time finding an image file to install on the computer. I ended up finding a guy on craigslist that was selling SSDs and he put yosemite on it for me. After that, the macbook was brought back to life and then gained a little performance from the SSD. He told me how to download whatever OS I needed/wanted to whatever media I would like. I ended up making a SD that has Yosemite on it, in case I ever need it again. Flash forward and I found another A1278 2010 MBP for pretty much free, the guy said the HD went bad and didn't fix it. So I got the hard drive that came with MBP #1 and installed Yosemite to that drive via SD card. Well low and behold that HD has Apple files already on it, because when I booted computer #2 it has a user named "CEO" of which I have no idea what the password is. How can I completely erase this HD and start from fresh? I was looking in the properties and couldn't find anything to wipe clean. I even tried to manually delete all the folders within the HD, but nothing happened. I'm going to give this one to a buddy, but want it to be a fresh install where he has to create his own user info etc. Let me know if that doesn't make sense. TL;DR I have a HD that wasn't mine previously and want to wipe it completely clean and then install Yosemite to it.