Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
Technically no, you dont need another copy and you won't get caught installing it on another Mac since there is no registration or DRM. But ethically you should purchase another license.
I dunno, I think its more legally than ethically. After all, the reason apple can afford to not have any sort of copy protection or anything in their os's is because 95% of all copies of OSX are legal (due to you needing to buy a hefty, expensive piece of machinery to get it )