The polyfill.js is a popular open source library to support older browsers. 100K+ sites embed it using the cdn.polyfill.io domain. Notable users are JSTOR, Intuit and World Economic Forum. However, in February this year, a Chinese company bought the domain and the Github account. Since then, this domain was caught injecting malware on mobile devices via any site that embeds cdn.polyfill.io. Any complaints were quickly removed (archive here) from the Github repository.
I’m not blaming the single person who did a mistake, I’m blaming the negligence of the companies that cut corners for profit, so most of them.
Your first comment read as if organizations where this happens couldn’t have bad consequences. Your new comment explains what you meant better, and I agree.