ALL CPU coins will run into this same issue if their value is good enough to attract the botnet criminals. You either have to live with their influence, come up with a way to slow or stop them like SPR, or drop CPU support altogether. XMR is a good example of another innovating coin (not even multi, just CPU) that was highly abused by botnets until its difficulty/market value drove a lot of its bots to greener pastures (ie: neos and other blake coins). It may or may not recover either...