In 2015, the New Jersey Attorney General’s office shut down a company called Tidbit that was offering website owners a way to mine cryptocurrency on the computers of site visitors. Authorities argued that this was illegal, on the same level as hacking, because Tidbit or website owners didn't ask for specific permission to carry out such intrusive operations.
JSEcoin seems to be offering this same service, already declared illegal by New Jersey.
I saw this same quote in the article mentioned in this steemit article: https://www.bleepingcomputer.com/news/security/malvertising-campaign-mines-cryptocurrency-right-in-your-browser/
I think JSEcoin is headquartered outside of the US but still, it seems to present legal problems. I wonder how it will turn out for them.