Security Code lockout with 10.9 upgrade

I had a customer come in with a 21.5" iMac Mid 2010. She had bought it on Craigslist with no hard drive in it. I formatted a new 1 TB hard drive and set it up for 10.6.8 and and cloned a system externally. Then dropped it in and all's well. The machine runs great.

She got home and tried to upgrade to Mavericks. It asked her for the security code which she did not have. She brought it back to me. When trying to start all I can get to is a screen asking for the code both on regular boot and "R" boot.

I reformatted the drive externally and put 10.6.3 back on it. Now when I try to boot I get a padlock symbol. Looks like Mavericks activates a request for a passcode and then locks up in the EFI firmware chip. This really worries me about buying any logic boards or older Macs on eBay. How can I tell if a passcode has been used? How can I get rid of it? Do I have to reprogram the chip? Do I buy a pre-programed one on eBay and solder it in, if so do I need a soldering work station or will a heat gun work? This issue could potentially be devastating. Thanks for any help.