 , most ransomware attackers preferred to use currencies other than bitcoin, with 44% of attacks in the first half of 2018 demanding Monero, which is highly private and difficult to trace, compared to 10% for bitcoin and 11% for Ethereum.In June 2011, Symantec warned about the possibility that botnets could mine covertly for bitcoins.Malware used the parallel processing capabilities of GPUs built into many modern video cards.