Which one is incorrect?

a$)$ Nowadays, ransomware is one of the biggest security problems on the internet

b$)$ Some ransomware infections start with someone clicking on what looks like an innocent attachment that, when opened, downloads the malicious payload and encrypts the network

c$)$ Washington says Pyongyang was behind a hacking attack against Sony Picuter Entertrainment in November, $2014$

d$)$ Traditionally, SCADA is not used in the distribution system such as Water supply, and Electric power distribution.