-the only method of getting the money back is using the key you manually wrote down -unless some hardware
Or a low-level rootkit.
was recording your computer or a camera was recording you, baring having someone take the piece of paper from you, no one can get your BTC
LiveCD is *not* enough! You should re-flash the BIOS/mb firmware/EFI firmware/etc if you want to be really certain of a secure system (or start with pristine hardware from a trusted (and competent) manufacturer [which is still no guarantee]).
Read this:
http://www.awgh.org/archives/27Also, access to source is not enough either if the compiler or interpreter (or any layer under them or your program) is compromised:
http://cm.bell-labs.com/who/ken/trust.html