Browsers, except Chrome recently [1], will ask the user if they want to run Flash. I do not believe that most people even understand the risks Flash brings.

[1]: Chrome stopped asking and won’t run Flash until they click though a couple menus to enable it.

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Edit: I just remembered that WebAssembly has JavaScript based polyfills. Disabling WebAssembly does not do me much good, as it will still run. No dialog can really stop that...