With Monero being relatively easy to mine compared to other cryptocurrencies, legitimate users and a bunch of nefarious users are working hard to mine the valuable digital currency. The value of Monero means that some of those nefarious users are rolling out massive botnets to shackle PCs into working for them. 
Proofpoint says that it has

Source: Hot Hardware – Massive Smominru Botnet Is Turning Windows PCs Into Cryptocurrency Mining Zombies