Last time I heard, none of the Reactors in the USA are connected to the internet for this reason.
Pretty much all modern PLC hardware is accessed, programmed and if necessary, viewed using a personal computer. The PC may or may not be connected to the internet - I'd say the vast majority are NOT.
Wrong.
See below findings.
Note - Hackers also get into ICS crucial server sys admin accounts via wireless SCADA system network vulnerabilities, or service vendor maintenance dial-up lines or FTP services.
Unheeded cybersecurity threat leaves nuclear power stations open ...
https://phys.org/news/2015-10-unheeded-cybersecurity-threat-nuclear-power.html Proxy Highlight
Oct 19, 2015 ... The report also found that power plants rarely employ an “air gap” (where ... in nuclear power plants were designed in an era before the internet ...
Researchers Hack Air-Gapped Computer With Simple Cell Phone ...
https://www.wired.com/2015/07/researchers-hack-air-ga... Proxy Highlight
Jul 27, 2015 ... The most sensitive work environments, like nuclear power plants, ... Usually this is achieved by air-gapping computers from the Internet and ...