Direct linking via a specific CDN was the problem. This is solved by bundlers, not caused by it.
The polyfill.js is a popular open source library to support older browsers. 100K+ sites embed it using the cdn.polyfill.io domain. … 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.
I actively do this with uMatrix - granted, I only block non-first-party JavaScript. Most sites I visit only require a few domains to be enabled to function. The ones that don’t are mostly ad-riddled news sites.
There are a few exceptions to this - AWS and Atlassian come to mind - but the majority of what I see on the internet does actually work more or less fine when you block non-first-party JavaScript and some even when you do that. uMatrix also has handy bundles built-in for certain things like sites that embed YouTube, for example, that make this much easier.
Blocking non-first-party like I do does actually solve this issue for the most part, since, according to the article, only bundles that come from the cdn.polyfill.io domain itself that were the problem.
Just went ahead and Googled it and I can find no credible source that he actually said these words at any time. So, if you’d like to bandy out that source, I think we’d all appreciate it.