People can guess private keys? Seriously? No one is capable of doing that genius. Many have tried to crack these keys in different ways(Brute force etc), but failed which is why a large portion of BTC is lost basically. Supercomputers could possibly crack them in the future, but it would still be really difficult.
Supercomputers can be the quantum computers which supposedly can crack coded and keys like the chicken eggs. That time can be coming but then again in parallel to this there can developed security measures to counteract the whole thing...so this can be just another opportunity to do business for security-focused software companies. I still believe though that it can be so difficult for any program to get into these private keys.